Maybe black voters would have delivered a handful of Southern states to Nixon.
I imagine you would have actually gotten a pretty similar county split to Reagan/Carter in 1980, as uncomfortable as that is for the "Dixiecrats were the first to switch to the GOP" narrative.
There would have been some major differences as compared to 1980. Nixon would have done way better with black voters than Reagan and much worse with Deep South whites, even compared to Carter's very decent showing with that group. Nixon also would have done a lot better than Reagan in New England.
My point is that Reagan did not win the Southern states that he won in 1980 by winning the areas that had supported Wallace in 1968. He won those states by thin margins due to suburban strength, and he lost most of the counties that the eloquent users of Atlas would now classify as filled with "racist hicks" - voters that went to Carter, per county results.
Well, Nixon only got 14% in Alabama and Mississippi in 1968. As Reagan just barely carried these states over Carter, he needed plenty of Wallace voters to do that, and he got them. Though yes, rural Southerners largely stayed with Carter; perhaps it was suburban Wallace voters in these states who would back Reagan in 1980 (and many of them had even voted for Ford four years earlier).
