I guess it depends how bad things get this year in this hypothetical situation that sees them bad enough to justify this kind of thing. If they play as expected and win 80+ games ROS, he obviously stays. If things actually get bad and they finish with a low-70s win total or something, it becomes harder to justify keeping JD for a 2018 run given that a down period will look inevitable if that happens, and a JD trade return gives them a huge head start on turning things around quickly.
I guess the other possibly is that they wear their big boy pants and keep their super-elite franchise player long-term.