I couldn't answer that, because he never existed in the movie universe anyways. so I do not know. The movie could never change different, with a character from the vitabu that were never created kwa Disney It's been 14 years since TLK 2 was released, anything like that can't change. I actually never heard of Kopa since last mwaka and he only exists in the books, he was never Fluffy nether. Kopa would never be in any films when he's not an official character.TLK films are good the way they are.
If Kopa - au any son of Simba and Nala - was in the story, I don't think they'd written Kovu in it at all. After all the most basic point of Kovu is that he falls in upendo with SImba's daughter after he joins SImba's pride, so that he could become who he can be instead of who his mother was trying to make him.
So what would happen to Kovu if Simba has a son in the sequel? My answer simply put: Kovu wouldn't exsist in the first place and the story would be perhaps entirely different from what it is now.
But that's only for the story matters. Because lion prides have one au two LEADER males, but it doesn't mean there wouldn't be zaidi males in general. A lion pride may have even 6 males. So in that sense Kovu wouldn't necessarely be a problem. But just for the matter of the story Disney wanted to tell.