Maclin has zero value if he's leaving.
Well this part isn't exactly true, and at best it's a highly subjective opinion. Maclin was a first round NFL pick, and has been pretty successful so far in his early career. He has suffered through a bunch of injuries, but has performed well when healthy.
There's plenty of destinations where he can end up and still have value.
I agree the overall trade is practically indefensible though - I'd
maybe trade Gordon for all of that (not likely), but adding McCoy make it silly - like I said it doesn't help the guy this season or in the future.
It's very odd though that a team would pull anything shady when he still has a great shot to win the league. If he's truly leaving, one would think he'd sell out to further help him win it all - not give away productive players.