The GM of Severstal said the reason he traded him was because he was going to the NHL at the end of the season, he's all but confirmed he wants to play in the NHL next season in interviews, every NYR source I've seen seems to indicate they believe he's coming over, the team probably would've traded him for Staal if they actually thought he wasn't coming over instead of what we gave up, and the ruble is completely in the tank.
There's a lot of information that indicates he's probably joining the Rangers. We can't rule out him re-signing with SKA, as they have the capability to offer him as much money as he wants, but he's probably not going to accept their offer.
That was then, if he found a nice spot in the SKA (by all reports Petersburg is a great city) lineup and they offer him great money, it may be he considers the offer. If he comes to the nhl later he has a shorter ELC, hence he will earn more in his career.
To be fair I am only speculating.