So if Glennon looks unbelievably bad on the Bears, and they sport an even worse record than 2016 by the end,
does Cutler get offered a job? Does that change the narrative of Cutler if we just totally suck?
No on both points.
Cutler has gone - he's not coming back under any scenario. Anyone wanting that to happen really has no love for the Bears (even if he proves to have been better than Glennon) because a young prospect offers far more upside than the return of an ex veteran player - especially one who didn't have the support of the fanbase in Chicago. It would be spectacularly misguided (and would never happen).
If Glennon sucks then most I assume are hoping that we have the future QB on the books - whether that's Watson/Trubisky/Kizer or even a Peterman/Dobbs. If we don't, then Glennon stays and we suck for the top QB pick in 2018.
As for Cutlers legacy - it is what it is and nothing will change that. If you thought he was under appreciated then that seems fine, if you thought he underachieved then I think that's fine too. He's gone now, so better to leave that debate behind and focus on supporting the new guy and hoping he is the answer or, at worst, he is holding the spot for the next great hope.