We pretty much have no money invested in the WR group. Even less once Thielen is gone at the end of the season. We have a promising 1st round rookie and nothing much else beyond that under contract once the year is done. At some point you have to pay the money and keep what you have if the production justifies the outlay. What's the point in losing it in the hope we find something similar in the draft, just because it will save some money?
The defense is in need of all the high draft picks and it's going to be hard to find someone as good as Johnson in the later rounds, so that leaves you signing JAGs in free agency with the likely outcome being a trashy WR group.
With that being said I would absolutely trade him if he made it clear he won't stay around regardless of the deal on the table.