The notion that 20% of Biden voters would’ve voted for Trump if Sanders were the nominee, as well as the notion that 20% of Trump voters would’ve voted for Sanders if he were the nominee are both ridiculous, in my opinion. Feelings about Trump were largely baked in, and the number of Biden>Trump>Sanders and Sanders>Trump>Biden voters is tiny at best (the former is overrepresented quite a bit on this forum.) Sanders would’ve done roughly the same, maybe he would’ve barely lost GA (just barely), but downballot races would’ve gone down similarly, give or take a seat or two. People are letting their feelings get the best of them when it comes to their analysis, unsurprisingly.
Probably AZ too.
I actually think Sanders would’ve pulled off AZ narrowly, albeit with a slightly different coalition than Biden (slightly less support in Maricopa, a bit more support among Latinos, particularly in Yuma and Santa Cruz.)
True, GA is the iffier one due to fewer Hispanics. But even if lost GA, I think there's a small chance he wins NC.