Good question. But probably a bit premature.
Not many companies spend the time and money to attend events like PAX once a game is out, particularly in the first month after release, since that is a crazy time of assimilating feedback and working on patches. The only reason I'd suspect they might come is because PAX East is practically in their backyard.
Watching the companies set up and run their booths at these events is a real eye-opener. The logistics and expenses can be crazy. It may all be fun and games for us, but it is work, work, work for them.
Even a bar party might not be too attractive. It's one thing to hang with your fans as they
anticipate a game. It's quite another to hang with them after the game is released, and they can corner you with their "constructive" feedback. LOL