If (and when) Datsyuk leaves, it will be on his own terms. It's pure speculation as to when and why, but I've seen other elite players make a move because the club doesn't get them the help they need to play up to the standards to which they hold themselves. It's got to be a grind for Pasha. A couple of times this year (last night being one of them), you could almost see on his face: "I have to do this, or no one else will... "
His daughter is in Russia after his divorce, so I can see him leaving to be near her. He's a freaking rock star over there, and can play wherever he wants for as long as he wants, and live like a king in Mother Russia. As if Feds wouldn't give up some precious body part, to get Pasha back?
From what I know of Datsyuk as a player, he will probably be loyal and retire a Red Wing, rather than go to some other NHL club. My heart couldn't take seeing him in another club's jersey, personally. I seriously doubt he's leaving because he's scared of being in the East.
I hope he stays a few more seasons, but like someone else posted, I don't entertain unrealistic (wishful) notions that he will be a Wing until he's 50. I think missing the playoffs, should that happen, will be a catalyst one way or the other re: his departure.