If a team just wants Byfuglien for next summer they could just way for the contract to be terminated. But Jets won't terminate until after the trade deadline, which is the deadline when your playoff roster is set (you can actually trade after the trade deadline, but then that player is not eligible for the playoffs).
If you trade for him now though its because you think he might be helpful for the playoffs.
I imagine it would go something like this: trade is a fifth and a conditional 2nd. If Buff doesn't pass a physical the entire trade is cancelled. If he does pass buyer sends over a 5th. If Buff actually plays more than, I dunno, 10 games for you a 2nd round pick is thrown in.
He apparently hasn't been skating so you're not getting him before mid-March on the ice, but he could be a factor in the playoffs for someone.