I'm convinced that Misha really doesn't know anything. Of course he wouldn't tell us if he did, but like you say, he'd be more cagey and 'maybe I will be back, maybe I won't, who knows'

But, yeah, there is nothing we can do, so we can just wait and see, and hope that Sera didn't lie to us when she said that Misha will be back. And that he will be back as Castiel.