RTF is a global modification that replaces all towns in the game.

would it be possible to implement healing based on the percentage of the defeated unit? for example, there's a stack of 100 peasants, and a knight kills 70 with the first attack, but doesn't heal. then, when he finishes off the remaining ones, he heals based on the percentage of the 30.

Added 1 minute ago

As far as I know, Heroes 5 isn't entirely canonical compared to 6 and 7, as the Ashan universe only appeared in them. So, the neutral Death Knights have no reflection in the canon. It's a completely different matter that the hero class of Necropolis also called Death Knights. Hence, the conclusion is that Death Knights are just a type of necromancer.

By the way, about heroes. What will the hero models be like?