Also, you have to win the majority of counties to win the governorship in Mississippi, right? That pretty much locks any Democrat out.
No, you have to win the majority of state house districts.
This is also a myth. You only have to win if you fail to win a majority of the vote. So this only affects the race in the scenario with a strong liberal 3rd party campaign(not unreasonable as Hood is white but Hood is getting black support in the primary anyway and race isn't everything for black voters.)
So considering how 2016 was a strong 3rd party year relatively it is unlikely this will affect the race but not impossible.