I'm not denying the characters' existence in the general TLK universe. This post speaks for the movie universe only.
Please forgive me the frustrated tone. No offense intented to anyone. For now this fandom has just made me so frustrated because it just can't draw a line anywhere when it comes to what is official/canon.
There's a reason why there are the different terms; canon, semi-canon, fanfiction. Because there's a difference and the difference matters. I personally welcome fanfiction with open arms into my interests in fandoms - but I do find it also awfully important that the facts are kept straight in official/canon vs. fanfiction. And in this fandom the facts are so messed up.
"Scar killed Mheetu! It is true! Just search google!" Since when was random Google search results the Truth? I think you'll find the truth a whole lot less dranatic. And "Zira killed Kopa and that's why-" Blah blah BLAH. Then why doesn't the film refer to any cub or murder with so much as half a word?! Perhaps because Zira DIDN'T kill a cub. "Why haven't they made a movie where they explain what happened to Kopa?!" Because nothing happened to Kopa for Kopa has never existed in the movie universe.
You know what I think is this fandom's problem?
"Mheetu,Sarafina's son by an unknown male is never mentioned in the movie. But he does exist! So what do you think is his story? Here is my opinion..."
As in that every character who has ever been mentioned in The Lion King universe in the slightest official shape or form - whether it was originally intented into a film or simply has Disney's stamp on it - has to have an official story for why they don't show up in the film(s).
In fact Mheetu doesn't exist and he doesn't have a story for not being in the movie(s) because he was cut out with no references. Hence, CUT out, not written out. And Kopa doesn't appear in the Simba's Pride film because he never existed in the first place.
Boring? Yes, I agree. But that's the reality of film making;
Mheetu is a victim of how lots of stuff is intented but then cut out as unfitting, unneeded, or just out of the way of better ideas, and thus not meant as part of the final outcome's universe in any way. Becomes non-existent without a story for it.
Kopa is just a fanfiction character which Disney holds copyrights for. Because he wasn't developed by Disney and he was evidently never intented by the film makers. He was created by non-Disney people after the film was released. Created him into the book universe for kids' amusement and Disney's profit purposes, which is very likely the only reason Disney gave its stamp on the books and several other books that contradict those books' content. (Being the evidence why the book universe is fanfiction stories and not semi-canon.) And thus Kopa got ignored and denied by all film makers and remains a fanfiction character who never existed in the film universe and so doesn't have a story for it.
There are no stories for the two characters' absence in the films. Mheetu just isn't there and Kopa is a never-was.
It's cool and fine if you want to create and share fanfiction views for why they don't appear in the films - those made-up stories may be even interesting. But for heaven's sake, they don't REALLY have a story other than that they just aren't/never were there. So please stop spreading the stories as official - because not one of them is, and please stop saying/giving the impression that the characters officially exist in the movie universe - because they don't.
There are many fans out here who actually care about the facts and discussing the true canon world - and even more importantly, when new people come asking questions they naturally want THE FACTS and not your personal believes, not your fantasy world mambo chambo and fanfiction visions.