Exactly. All mentors are contractually obliged to perform a noble sacrifice. And they tend to return in some form. Gandalf (ressurrected because God said so), Dumbledore (meets Harry in purgatory), Obi-Wan (Force ghost), etc… Actually, this makes me realize there is no such figure in Avatar, one of my go-to examples of a fantasy epic like the other three, unless you count that one monk Aang liked who died in the Air Nomad genocide.
This is Joseph Campbell territory. It’s an archetype.
Avatar has hundreds because they’re all contained within him.