Fumbling does not eliminate all past achievements, that's ludicrous. More so given that fumbling has never been a problem Carson has had.
Is there a competent back in the fold behind him? Certainly - there are two, actually. But neither have run anywhere near to Carson's level yet or put Carson in jeopardy of losing his starting spot based on what they've shown. I'm not saying it's impossible, but to this point neither Prosise or Penny (even looking better than he did last year) has performed anywhere near to the level Carson has, with anywhere near the same consistency.
If Carson keeps fumbling, of course the team rethinks it's approach. Stupid not to, you want to win, period.
That's not the point here. Here is what you said:
Carson has shown he can absolutely be counted on in this game. Carroll gave him almost every carry in the game.
And Carson put up impressive numbers all last season and been pretty damned dependable in all aspects of the game this year.
It hasn't been one game where he's proved it -- Top 10 back last year, Top 10 back this year so far.
To use you own point, one or two games with a fumble -- especially where that's never been a prior concern -- doesn't change his proven ability, performance, and the stats he's put up.
Stud. Period.