My guess is either Neville Longbottom or Pomona Sprout. They can't both be Herbology professors, and likely both of them are qualified to teach either Herbology or Defense Against the Dark Arts. They must have split in some way, possibly both of them teaching half of either class.
Of course, it's possible that Professor Sprout would have retired by that time, but I hope she hasn't.
The sad part is, had Remus Lupin survived, he would have made an awesome DADA teacher again, as parents would be more likely to accept him as a professor after the War, having seen that there are much worse things a Hogwarts professor can be than a werewolf.
The real question, though, is who would teach Potions? It seems there are very few people qualified for that position, Professor Slughorn would be retired again, and Professor Snape has died.