Yeah, it seems that the writers forgot about those leopards who "were in a bit of a spot" but for the fun of theorizing I actually had an extensive talk with Lyonize and ABB about this once, and we came to a conclussion:
There used to be some leopards in the Pridelands during Mufasa's reign, but they became loyal to Scar, just like the Outlander lionesses, and so they were banished as well. Evidence of this can be found in the TLK SNES/Genesis game, where there are leopard enemies fighting along with the hyenas.
Attachment 897
Wether you consider the game canonical or not it's up to you, but hey, at least the show made it a possibility by having a lava river in the Outlands, just like in the game