Will Guy Scott be able to run? It'd be pretty weird for an African nation to elect a white leader.
No not according to his own statements. Besides 1) his wing of the party has lost the internal power struggle during Sata's illness, so he wouldn't be nominated even if he was eligible and they would disregard race as a factor 2) at 70 he is rather old. Two of five Zambian Presidents have now died in office of natural causes and I think the major parties will go for someone younger, this will likely also rule out ex president Banda from MMD, who is also 70+.
Mwanawasa wasn't all that old when he died in office, only 59