invadersmustdie

First of all. I would like to say that my english is pretty bad Ok here goes my question: I wanted to know if there is a way to make an NPC (such as luke) Invincible. Because i love having NPC´s Fights in Single Player but i can't stand having to spawn Luke everytime he dies. I tried to modify his health in the ext_data/npcs file but when he falls from a high place he seems to "freeze" and he doesn't move anymore like he's dead or something. Its weird. Any help? I forgot to say that the game is Jedi Knight II Jedi Outcast sorry if my english is horrible.