I don't know whether the same rules regarding CHL players and ELC's apply to imports as they do to domestic players. If they do, then I'd fully expect Sushko back with the Attack next season as I can't see him making, much less sticking with, the Flyers. Assuming the rules do NOT apply to imports and therefore he could technically play in the AHL...I guess I would question why the Flyers organization would want him in the AHL next year. Sushko has had a great campaign for sure, but I don't think I would go as far as to say that he has nothing left to prove in the OHL. He could be a real leader on this Attack team next year.
If I had to guess, and again I don't know all the rules about this, I wonder if the signing now would enable him to play with the Flyers' farm club in the AHL playoffs once the Attack's season is over. Just checked the AHL standings, Lehigh Valley is second place in their conference. Looks like they could make a long playoff run, while Attack could be done in 1-2 rounds, depending on goaltending/coaching.