All-Star Comics: Starman and Mid-Nite telling their respective love interests about their secret identities is hinted and teased again and again as situations make it seem it's necessary, but it never comes to fruition...until Wonder Woman tells Starman's girlfriend when he goes missing for a bit, and the change sticks.
The Riddler reformed in 2006 and became a private detective. Not only is he good at it and indulges his obsession a bit, but it changed him morally for the better. Of course, a few years later, a severe head injury sent him right back to his villainous ways.
Harvey Dent is a victim of this. No matter how many times his face and sanity are restored, soon he is driven back to his (half)disfigured face and insanity, even in some out-of-mainstream-continuity stories, like Batman: Black and White. In an Alternate Future from Frank Miller's limited series Batman: The Dark Knight Returns, only his face is restored, not his sanity. From Bad to Worse: His good side vanished, leaving him all "normal" outside and all monstrous inside.
Grant Morrison acknowledged this in his run, where Bruce was temporarily "killed off" during Final Crisis and Batman R.I.P., leading to Dick Grayson becoming the new Batman. Morrison has flat out stated that he knew there was no way in hell DC and Warner Bros. would ever let him permanently replace Batman, so he purposefully structured the story in such a way that left the door open for Bruce's return. He also admitted that he killed off Bruce's son Damian for similar reasons, since having a kid clashes too heavily with Batman's iconic "brooding loner" image. Damian has since come back, however. (It helps that he's even more of a brooding loner than Bruce.)
Barbara "Batgirl" Gordon eventually had this happen. In the The Killing Joke, she was shot in the spine by The Joker, rendering her permanently paralyzed. Barbara then took on the persona of Oracle, working behind the scenes to aid the Bat-Family and Justice League of America with her hacking skills and computer expertise, and led the Birds of Prey. But after the 2011 reboot, Barbara was back on her legs as Batgirl.
Averted with Dick Grayson, the original Robin, who became Nightwing and was succeeded by several others in the role of Robin.
There are stories where Jim Gordon is removed from the post of Commissioner only to end up back in the post. While naturally some of these are the result of ongoing subplots such as the early stuff with Hamilton Hillnote replacing Gordon with fellow Rupert Thorne crony Peter Pauling and only reinstating Gordon after Thorne was busted and Pauling killed and the Batman comics between Knightfall (including Prodigal) and Contagionnote Gordon was pissed about Batman appointing Azrael and Nightwing to fill in without telling him, resulting in Gordon refusing to trust him further. Then Mayor Armand Krol, who'd been saved Batman and approved some of Azrael's actions as Batman, demoted Gordon and appointed Gordon's then-wife Sarah Essen to replace him and rather than take it, Gordon quits. Contagion ends with Gordon regaining his trust in Batman and new Mayor Marion Grange reinstating Gordon, others are done after other stories.
Officer Down saw Gordon resign after getting shot (though the decision was based more on his age and the fact he missed his second wife, Sarah Essen, than the fact that his shooter seemed to get away with it). That was the status quo for five years until Face the Face, part of the One Year LaterTime Skip of Infinite Crisis, which saw Gordon return to the role of Police Commissioner, (as well as Harvey Bullock return to the force after being forced out by Gordon's successor, Michael Akins, when he got wind that Bullock sold out Gordon's shooter to the mob and Harvey Dent becoming Two-Face after his face was fixed in Batman: Hush). Despite his name being cleared, Gordon wasn't reinstated in the end of Batman Eternal and even wonders what he'll do now, a Sequel Hook to Superheavy, where he becomes Batman after Bruce's presumed death in Batman: Endgame. Superheavy not only ends with Bruce once again as Batman, but Maggie Sawyer, who'd become Commissioner during the final issues of Eternal, returning to the MCU and Gordon being reappointed Commissioner. This would finally be broken once and for all with The Joker (2021) being his final case as part of the Gotham police force and becoming a Private Investigator.
The course of Superheavy and DC Rebirth would also see the events of Eternal and Endgame undone as Alfred gains a new hand after the Joker cuts it off in Endgame and Bruce regain control of Wayne Enterprises, Wayne Manor, and his fortune after losing them in Eternal.
Batman villains thrive on this policy. The Joker especially, who has a trope named after him. He can kill and destroy as many lives as he wants, and all Bats does is punch him a few times and send him back to an easily escapable prison/asylum. He'll always be there to menace the Bat, and the ramifications of this continual (and destructive) cycle have now pretty much became a core aspect of their dynamic.
Superman's comics played it mostly straight for decades: Superman would never choose between Lois Lane or Lana Lang, Lois would never learn his secret, Lex Luthor would never turn over a new leaf permanently... unlike Supergirl, whose early Silver Age status quo (Superman's secret weapon living in the Midvale Orphanage as Linda Lee, who always failed to get adopted or talk her cousin into going public) was forever changed in The Unknown Supergirl, and remained in constant flux since then. Nonetheless, except for some changes during the Bonze Age (Clark Kent getting a new job in Kryptonite Nevermore, or managing to enlarge the Bottle City of Kandor), Superman's life would remain stable until the 1986 reboot. Ironically, the tables would turn from the 90s onwards, when Superman and Lois Lane got married and had a child, whereas Supergirl would remain stuck in a "Will Earth ever feel like home?" loop.
Since Flashpoint, Superman's secret identity has been revealed to the world twice, and both times it got undone after about a year to kick off a a "back to basics" era: the first time by a complicated procedure involving his apparent death, a fake — and apparently perfectly human — Clark Kent who believed the whole "Clark Kent is Superman" thing was a sting operation he and Supes had set up, the pre-Flashpoint Superman (who had been hanging around under the radar since Convergence) merging with the spirit of the dead version, and probably a bit of Cosmic Retcon around DC Rebirth; and the second time by Lex Luthor using Manchester Black to wipe everyone's mind, and make learning it again fatal — the Justice League and Clark's family (caped and otherwise) have protection from this sort of thing, so they still know.
Cyborg frequently falls victim to this. Anytime he regains his normal human appearance (or at least gets a sleeker, less monstrous form), it's always undone within a few years.
Green Lantern: Guy Gardner lost his Power Ring after it was destroyed by Parallax. Guy went on to get a full rework, including new powers, a new look, a new supporting cast and a new job. This lasted for several years—about a year and a half of which was actually in his own ongoing monthly— until Geoff Johns wrote Green Lantern: Rebirth, which snapped him back to being a Green Lantern.
Kingdom Comelampshades this. Wonder Woman's entire purpose was to come to America and bring an end to warfare across the globe. The problem of course is, thanks to this and Reed Richards Is Useless, she'll never be allowed to make any real progress in this mission. Thus, we cut to a few decades later and find that she's been exiled by her fellow Amazons precisely because she hadn't made any headway in solving this problem.
Traditionally Wonder Woman is the exception to this concept in most regards. Her original run had her first recurring villain turn into one of her most stalwart and loyal allies, the United States signing a treaty with the Empire of Saturn and setting up casual transportation between Saturn, Venus and Earth and that was all published before the 1940s were out. Both the Golden and Silver Age versions of Diana were eventually married to Steve Trevor with the Golden Age one losing her immortality and every Crisis is taken as an opportunity to twist and alter her origin and parentage. On a less character driven note her costume is also subject to frequent alterations, and always has been.
Despite The New Champion of Shazam pushing Mary Marvel as the new hero, Shazam! brings back Billy Batson as the main one with the powers. Downplayed in that Mary is still "The New Champion of Shazam", just that the troubles from Teen Titans Academy have been fixed.
The above case of the Kents' secret identity being restored, despite a big part of Jon's tenure as Superman being him not having a secret identity. This was expressly because the writers felt it was a more classic approach.
Supergirl's redesign courtesy of Woman of Tomorrow which included pants and shorter hair were kept for Dark Crisis, but her long hair returns here.
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