Nala shrieked as Kula went down. The hyena matriarch had bitten Kula's neck. Kula struggled to breathe.
"Kula! Kula!" Nala screamed.
"I'll... I'll be... I'll be okay," Kula coughed.
And without another word, Kula's life vanished. And Nala knew there was no point in trying to revive her, for the lively little cub was never coming back.
So yes, in my theory, Kula was killed by a hyena, which is why she never appeared in any of the movies. Just my theory, of course. You can find it in my fan-fiction as well, it's called "Light of Grief." Here's the link:
viewtopic.php?f=8&t=38827
It's still a work-in-progress but I'm still working on it.

Kula and Nala are (c) Disney
Art is (c) Iri



