I would'nt keep him, he score like 5 goals all season. He looked decent when playing (the few times I watched Fulham), but looking a decent player when on the pitch isn't everything if you not producing the goods you paid to produce....goals!
I don't see why he wouldn't move even if he knows Hull destined to get relegated. He is not garaunteed to be a starter at Fulham this coming season, Hull would probably improve or at the very least give him parity with his current salary and he should have more oppertunities to play with them and therefore potentially score more goals than last season.
IMHO as long as he gets a half-decent goals return, even if Hull are relegated he should find another lower-tier premiership side willing to take him on the following season.