IMO, Gordon might do well to take that last year at $34 million. I don't think he'll command a huge offer in 2020, but OTOH, with the injury he sustained, he knows that his career is fleeting and may bolt for greener pastures if someone offers him a Horford type deal. But I don't think he'll get even that.
Regardless, if we're in the hunt, no way should we trade him. The only way it should be considered is if the season is a total loss. Hayward with a few months left on his deal isn't going to fetch us very much, so disrupting whatever we have going would be foolish.
There's also the possibility that Gordon totally becomes the player we hoped, wants to sign here for the rest of his career, meshes well with Kemba and Tatum, and Ainge does something like trade Brown. There's simply too many variables to do anything other than make a wild guess.