How do Warcraft characters in lore actually get perma-killed?

Like when players die we just run back to our corpse and we come back to life. Gamon even hinted at having been killed thousands of times by Orcs in that latest sound clip. So I don't understand how people act like we can kill Garrosh and he won't just run back to his corpse 2 minutes later and be like "whatever" - ? Does anyone else ever wonder about this? Or did Blizzard explain why characters like Illidan, Deathwing, Garrosh etc. can't just self resurrect somewhere along the lines?

I didn't find the right solution from the Internet.

References:
I didn't find the right solution from the Internet.

References:

Brand Advertising Examples