I'd roll with the assumption that if Sanders was going to win, he would have put some investment into the South. He would not have won there, but for simple momentum reasons he couldn't avoid the South like he did irl. Maybe if he could hit 35% in AR and GA, 25% in AL and MS, 30% in LA and SC, and 40% in VA he would have not had the crushing blow to momentum. Also he would have gotten some more delegates.
Momentum didn't really matter. Sanders could have won by 1. tying with non-whites, or 2. getting to 60% of the white vote.
Option 1 would produce a much different map than the result. Option 2 would see Sanders's winning margins intensify across the North.
If Sanders did get 60% of whites, the map would have looked like this: