In Sockbaby Part 3, Sockbaby's plot was wrapped up, and he left for heaven or another universe or something. He doesn't appear at all in Sockb4by, which just focuses on the further adventures of Ronnie and Burger.
Other than being her TGWTG handle, have you ever heard The Nostalgia Chick being called her username of "The Dudette"? Even the url on the website was changed to "Team NChick".
The title of The Joker Blogs originally referred to The Joker's treatment tapes at Arkham Asylum being put up on YouTube (something the Joker planned to occur) in a 'blog' format, occasionally featuring updates with tasks for the 'goons' (fans) to do. As of the end of the First Season (around the start of the "Find Patient 4479" arc words), this is no longer the case since the episodes afterwards are in less of a 'blog' format and focus more on the plot.
Barney Bunch was originally made when Barney hate was still at large, but soon coming to an end. Today, most Barney Bunch videos feature Drew Pickles as the main character instead.
The first Demotivational Posters were cynical parodies of motivational posters, bearing messages about your inevitable failure. Following Memetic Mutation the same style of image is now used essentially as a one-man caption contest, keeping the name but rarely trying to demotivate. Some of them even depict highly awesome scenes with an enthusiastic caption beneath, thus being anything but demotivational!
Master Chief Sucks at Ordering stops being about Master Chief sucking at ordering things after the third episode. However, the series (and its episode titles) continue to reference the fact that Master Chief sucks at doing things. The reason the show wasn't simply called "Master Chief Sucks" to avoid this problem was presumably because another series already used that name; said series would then be permanently renamed to Arby 'n' the Chief.
Some people choose usernames that reference a series, then later on disown the series, especially in fandoms with poor reputations.
David Mitchell's Soapbox was originally a pun on the fact that it was sponsored by a brand of men's cosmetics. They withdrew their sponsorship at the start of the third series, but the title remained.
For a more general example, football forums have had Adaptation Expansion and football is only part of their schtick/USP; it still remains, probably due to the Grandfather Clause, but the term is an otherwise artifact title in general.
Although anyone can still upload documents, WikiLeaks stopped allowing people to edit them afterwards a long time ago, so it's no longer truly a wiki.
Some blogs on SB Nation, most notably the Toronto Maple Leafs' Pension Plan Puppets - it referenced how the Ontario Teachers' Pension Plan owned most of the team's parent company, but they have since sold their share. One at least confesses the nostalgia outfront: the Washington Wizards one references the team's previous name, Bullets Forever.
Textfiles.com started out as an archive of old text files (mostly from the BBS era of the '80s and '90s), but now has lots of content that isn't a text file.
Before Facebook was the social networking phenomenon that we know today, a "facebook" (or "face book") was a popular colloquialism for a university's student directory, which gave college students an easy way to look up one another's contact info. Mark Zuckerberg originally created his website as an online version of such, annoyed that Harvard University was taking too long to comprehensively move their student directory online. By now, Facebook has been open to the entirety of the public (not just college students) for around a decade, and the addition of Notes, "Like" buttons and status updates has made it far more than a simple tool for sharing information.
The That Guy with the Glasses website is still subtitled "Home of '5 Second Movies' and 'Nostalgia Critic'", and even the HTML title of the main page is "5 Second Movies". The last "5 second movie" published was in October 2009. It's pretty safe to say that the website has not been famous for the 5-second movies for a long, long time.
Lonelygirl15 doesn't quite fit after Bree's death, seeing as "Lonelygirl" refers to her.