If Fields misses 3-4 weeks, I'm not sure if his Bears career can be salvaged unless he comes back and demonstrates conclusively that he's an elite QB for the rest of the season.
If the Bears go 0-4 or 1-3 in his absence, they are going to be right in the thick of the number 1 pick discussion. If the Panthers continue to be the worst team in the league they'll be in that same discussion. If the Bears are 1-9 or 2-8, Flus's time will be pretty much over and they will be looking for a reset. Fields has shown flashes of being a great QB, but not nearly consistently enough to feel comfortable moving forward with him. He has also missed time in all 3 of his seasons due to his style of QB play. A 1-9 Bears team with likely 2 top 5 picks in the one of the deepest QB classes in years (apparently) is not going to commit to Fields for next year much less long term.
I know all of this is obvious to most, but just spelling out how this injury to Fields is probably the beginning of the end.