Sanders can theoretically afford to do as bad (or at least close to it) as he did in the Confederacy: as long as he keeps the Southern periphery in check, it's fine (not to mention CA's effects). Clinton won TX 2:1 in 2016: even if Sanders loses slightly, it's really not a big deal, as he'll be taking 50+ delegates net away from a candidate like Biden. The only major contest where he's likely to get rat-f[inks]ked is FL.
Little known fact: Sanders won more delegates outside the Confederacy in 2016 than Clinton:
Non-Confederates:
Sanders 1448
Clinton 1432
Confederates:
Clinton 700
Sanders 332
This is why the other candidates need to stay in the race to deny Sanders the majority of the Non-Confederate delegates.
The Confederate delegates are already strongly Anti-Sanders.
Based on the South Carolina results, we can conclude with certainty that the undecided voters or late deciders are Anti-Sanders and that they will break for Biden. That means that Biden may even win Texas.