Maybe as a little feature in expert mode all mobs except blockheads, dodos, donkeys, unicorns and fish should heal. Cave trolls, sharks, dropbears and scorpions would be able to heal if not hit within a limited amount of time.
This is based on master mode of breath of the wild.
if you do not attack a mob within 5 seconds it will start healing fast.
it will only take them at least 10 seconds to heal to half health and another for complete health.
Sound like a good idea?