It makes practically zero sense for Hayward to do any favors to the Celtics that would somehow benefit what is likely to be one of his major competitors at that point that the Hawks might become contenders.
And Hayward holds all the cards here.
I did say "practically." There is one and only one way that it makes sense, and that is if a 5th year is put on the table (which obviously would be something a 30 year old would have to get giddy about).
Hard to imagine that could be the case. Not impossible, of course, but highly improbable.
It, to me, is highly improbable then that there would be any trade mechanism to the transaction.
Here's the other misnomer about Hayward that probably needs to be quashed... he's likely going to get minutes at both SF and PF... at least, that's how he's been used in Boston most recently.

So, any talk about him gumming up the situation on the wings seems to not actually be well-grounded.