Stafford had a noticeable jump in his productivity back when OBJ was added to the offense and we were blowing out the Bengals early in that title game before his knee went out. And he had the same type of jump with the addition of Adams. So it's a no brainer to have him play out his second year with us.
Also I'll add that Adams has his weaknesses. He hears footsteps over the middle, which keeps him from being in that true elite range. He has concentration drops too. But his impact on Stafford has been undeniable so this is a really easy question to answer.
If I were in their shoes what I'd do is I'd make sure I draft a big wideout for outside the hash, or failing that one of the average sized types who offer returns. That way there's a young addition in the pipeline, and he can pick Adams' brain because the dude has been around and knows his craft. Basically if you don't load the weapons on offense then you are wasting Stafford's final years. This is why I am so focused on WR fit for Stafford as well, with the bigger options. But the main thing is that he's got plenty of weapons out there to throw to even if one of them misses some time.