The news today that Dean Ambrose has chosen not to renew his contract with WWE is a major story in a month of huge stories. It is arguably the biggest potential departure of a top WWE star on their own accord since CM Punk walked out of WWE five years ago in 2014 (which also happened to be at the post-Royal Rumble episode of RAW).
As is the case with every departure, a lot of fans are asking if the whole episode is a work. It should be noted that WWE has never publicly announced a release that ended up not being legitimate. Days after the Nexus (Daniel Bryan, Wade Barrett, Justin Gabriel, Michael Tarver, Skip Sheffield, Darren Young, Heath Slater and David Otunga) debuted on RAW in June of 2010 and attacked WWE talent and personnel, WWE announced that Daniel Bryan had been released. Most people thought that the announcement was storyline, however it turned out to be legitimate, as Bryan was fired for choking ring announcer Justin Roberts with a tie during the attack. WWE re-signed Bryan months later.
WWE has publicly announced many releases to the media and on their website, and there has yet to be one that was to further a storyline.
As for a talent not renewing their contract, Vince McMahon famously announced on RAW in November of 1994 that the company couldn't come to terms on a new deal for Randy Savage, and thanked him for his contributions. Savage never appeared in a WWE ring again, and made his WCW debut a month later.
In a situation similar to the one with Ambrose, WWE announced on their AOL channel (remember those?) in early 1996 that Kevin Nash, then wrestling as Diesel, would be leaving the company. Nash still had several months on his contract, and not only would he work a big match against The Undertaker at WrestleMania 12 during that time, he also would feud with then-WWE Champion Shawn Michaels. Nash was with WCW a month after his feud with Michaels ended.
It should be noted that I don't think that this is a work. But there was that one time...
In July of 2011, CM Punk was getting ready to face then-WWE Champion John Cena at the Money In The Bank pay-per-view for the title. The storyline was that Punk's contract was expiring, and Punk was stating that he would leave the company with the belt. Punk got into some hot water that month when video surfaced of him screaming at a fan at a live event in Australia and telling the fan that he has a vagina and is a "h-mo." Punk apologized and said that he was glad that the video was made public, saying, "I'm embarrassed. I own up to being a total douche in this situation and I offer a sincere apology to anybody I hurt with careless words."
The incident caught the attention of GLAAD, who said that they were in talks to provide training to WWE wrestlers and on-camera talent. According to GLAAD, WWE officials told them that Punk's contract was expiring soon, he would not be immediately renewed, and that he would no longer be with WWE as of July 18th, 2011, the day after Money In The Bank.
"This departure is not part of a storyline," WWE told GLAAD. "He is contractually leaving the organization."
Instead, Punk defeated Cena and remained with the company until 2014. For what it's worth, Punk claimed in an interview with Bill Simmons that he didn't re-sign with WWE until the day of the Money In The Bank pay-per-view.
So while WWE announcements have almost always been legitimate, there is one exception.