There are really only three options re: Flacco.
1. Keep him. Try to stack as much talent on offense as possible to get as much out of him as possible.
2. Phase him out. Draft a guy in the 2018 draft, make him sit behind Flacco until he takes the job and makes Flacco the highest paid backup QB in NFL history.
3. Cut him. Take on that huge cap hit, try to play money ball til 2020 then start anew.
My guess is that we'll see a mix of 1/2 since they aren't mutually exclusive. In 2018, I doubt that they'll be in the Darnold/Rosen range, but they could probably come away with a guy like Mason Rudolph in the 2nd/3rd.