Ever since all of the negative press surrounding Diablo 3 Jay Wilson has been oddly quiet. I believe he possibly could have been fired from the following reasons, Large amounts of players quitting, Launch issues, in game issues, community backlash, refusing refunds, Korean officials raiding blizzard offices, etc.
This is the first blizzard game that has tarnished their reputation badly, so it would be understandable if they were upset with him.
His twitter account has not been used since June 19th ( http://twitter.com/Angryrobotics/ ), and The last communication he has had with the playerbase was on reddit june 6th.
They probably just asked him to keep a low profile so as to not further fan the fire. Just look at Bashiok, whatever the guy says gets turned into a meme and reposted into infinity. If Wilson posts about personal stuff, people will think he's not working on the game. If he posts positive stuff about the game, it gets turned against him. If he refutes the criticism, people will have a massive fit. Shutting up and appearing very concerned is the best thing he can do right now. They probably won't fire the game director 2 months after the release while the future of the game is still very much uncertain. I doubt he will be attached as lead designer in the future though
Jay Wilson didn't sell 6 million copies. Diablo 1 and 2 + the blizzard brand sold that amount. It's what happens now that will get pinned on Wilson. You can only perform a bait-and-switch once. A company like Blizzard has much more interest in long-term life for a franchise than a smaller one would. You're right, the vocal minority won't have an effect on Wilson career, but a massive player emmigration, frozen RMAH and low expansion sales will without a doubt.