NHF – new heroes for Heroes V 3.1.

If he's going to be resurrected in the Overworld, then who will the undead and bone dragons be? By the way, is it not strange?

Implying that a moving skeleton, which doesn't even have the slightest semblance of muscles, is a perfectly natural thing.
Is there a resurrection spell in the game? Yes. Does it bring a corpse back to life? Yes, it does. Is there healing magic in the game? Yes. Does it heal serious wounds, quite possibly even restoring seemingly irreparably lost pieces of flesh and muscle? It's possible. Are there spells related to controlling souls in the game? Yes. So, if desired, one can justify the existence of some unique individual who created a ritual that brings long-dead people back to life by restoring their bodies and returning their souls to them. The problem is that if this is theoretically applicable to zombies and skeletons, then using it on vampires and liches, who voluntarily underwent rituals, seems rather strange. However, raising liches from the corpses of mages also doesn't quite fit the lore, and it is present in the original game.