McCann has a team option next year for something like $13 or $14m, and then he's a free agent. So while they could in theory cut him loose this offseason, it will (and should) be a no-brainer to pick up the option year.
It's dicey after that. He'll be 30 years old in 2014. Signing a 30 year old catcher to a long-term, expensive contract is a bad risk. He'll want to come back here, but it'll also realistically be his last chance to get paid. I have no idea what will happen with him.
The coldly rational thing to do is to pick up the option year and then shake his hand and wish him well. I can't see it playing out like that.