Okay, I know I'm not the first person to think of this but anyway. Lets look at the facts. The hyena numbers range throughout the film. The numbers are in some scenes like that:137, 149, 76, 83. So the estimate number of the army would be 150. Not 3,000 or 4,000 as some fans tend to say. That is biologically impossible! How can the hyenas get along like that! Even at 150 it is a miracle. Now during the fight on Pride Rock we see hyenas fleeing. That drops the number of the army. When Scar is cornered you can see only 10 hyenas (trio excluded). 10 against one. That still outnumbers Scar. But we forget that the hyenas want revenge. Don't you think they would kill Scar instantly? No, they would bite deeply to hurt him but not kill him,yet. Plus, we are talking about a lion, not a human. The hyenas couldn't break his neck because of the mane. You can't break a neck if your mouth is filled with a mane, huh? Scar probably kicked one of them off him and the hyena fell in the fire that was surrounding them. His cries distracted the othes who started panicking (animals are generally VERY afraid of fire). Some hyenas escaped, other perished in the fire. Scar was wounded and chances of escaping weren't good. But do you fans remember in TLK2? When Kiara ran in the cave and found this hole at the back of the cave to escape. What if Scar found a similiar hole? He could have gone in, waited for the fire to end and then ran for his life. From then on, he might have found help.
I know this theory sounds complicated but I don't want Scar to die!!! What else do you expect from a Scar fan!