This is sort of an inane argument. I truly believe that Stoudemire will suffer without Nash and vice versa, but probably not as much as we would like.
An assist can only be credited on a made basket, so while Nash would be responsible for the delivery, there can be no assist unless Amare makes his shot. So both are responsible for a lot of each other's stats. The question is if both of them will continue without the other? I think Nash right now would fare better simply because he has better finishers around him now than Amare has passers.