They could just make you dead when your HP hit zero. How would that be?
It can certainly be a challenge, but I can't say I have so far found that it is outrageously difficult to get an unconscious player back up and into the fray.
Ideally, whether the AI does this or not should depend on the intelligence and/or behavior of the attacker. Animals tend to keep after prey until they're dead. Intelligent opponents might think it best to finish off any downed foe lest they get back into the fight (like you, me and probably everyone else would do). Or maybe they would see it best to go after the next immediate threat. Varied AI on the matter would be best.
