This happens regularly. Wrestlers leave the company, which is very rarely acknowledged on the air; the sole reference will generally be in a short corporate press release stating that they and the company have come to terms on their departure and that WWE "wishes them the best in their future endeavors" — leading to the popular Fan Speak term for a wrestler being fired: being 'future-endeavored'. They may be taken off the air prior to leaving, to lower their 'drawing' value. Usually this happens to guys who work the lower matches, and so flies under the radar, but occasionally even a big name will simply vanish. For example, Sable, who was extremely popular in the late '90s, abruptly vanished from programming — because she sued the company. Similarly, Eric Bischoff was taken off the air in WCW for his inept management, and his on-air departure was never acknowledged, which made it even less understandable when he returned in April 2000.
A particularly egregious example was when wrestling's first megastar Hulk Hogan left the WWF in 1993. After losing the WWF title to Yokozuna at King of Ring, Hogan was never mentioned again until wrestling started taking on more 'realistic' storylines.
One of the worst examples of this happening was the managers of "Stunning" Steve Austin after he first entered WCW in 1991. When he debuted, he was accompanied by a brunette named Vivacious Veronica, however after a few weeks she was replaced without explanation by a blond called Lady Blossom (who was Austin's then wife and former WCCW valet, Jeannie Clark), about a year later she disappeared and Paul E. Dangerously (AKA Paul Heyman) took over the job of managing Austin.
Madusa and Col. Robert Parker both fit in there somewhere too.
When Berlyn (WCW mainstay Alex Wright, repackaged) debuted, he originally came out accompanied by three bodyguards and a pretty female interpreter named Uta who was getting surprisingly popular fairly quickly. Then Uta and two of the bodyguards disappeared about a month into the character's run with absolutely no acknowledgement.
A recent example; in late 2010, after his Face-Heel Turn, Tyson Kidd appeared on RAW with a new bodyguard, 7-foot developmental talent Jackson Andrews. Andrews, for all of his size and intimidation, was as green as grass, and after about 4 weeks, following Kidd losing a match to Mark Henry, Andrews sustained a World's Strongest Slam from Henry and returned to developmental limbo, where he would be released soon after, never to be mentioned or talked about again.
Happens a lot with valets, for instance, Carlito's temporary bodyguard-or-something, Jesús (as in "Hey-suess"), who, in Kayfabe, stabbed John Cena in a night club. He then faced Cena in a street fight at a PPV, which resulted in Jesús getting beaten within an inch of his life and never being mentioned afterwards.
If not for CM Punk's throwaway lamentations, those who don't check WWE corporate statements would probably be ignorant about guys like Festus/Luke Gallows, Mike Knox and Vladimir Kozlov getting 'future endeavored'. Nor would they be aware of John Morrison, Melina Perez, Gail Kim or the Bella Twins just up and leaving.
Or, in the case, of the Bellas, returning out of nowhere either.
Possibly justified example in Chris Benoit after it was discovered he had killed his wife and son before committing suicide. DVDs prominently featuring him were discontinued (some permanently, such as his biographical release), commentary for certain matches featuring him were edited, and his name was removed from many pages on WWE's website. As of late, they've steadily begun reversing this course, but never so far as to even indirectly mention him on TV.
Remember the guy who won Tough Enough? Andy Leavine? A few videos aired for hyping him up, however they stopped and he was quietly released months later, never to be mentioned again.
Since walking out in January 2014, CM Punk has become one of these. His first mention on WWE television since then was the March 2014 episode of Raw where Paul Heyman came out to his music. Later on, however, at Payback 2014, when the crowd was chanting Punk's name, she told Daniel Bryan, who was in the ring with her, that they wanted Bryan to quit as CM Punk had.