The cub at the end the creators named "Fluffy". Kopa was simply a character from the Six New Adventures. But really it's all open for fancreations. It's [mostly] non-cannon anyway, so it could be whatever you want. Lol

he did not die or surive. he is not the the cub you see in the end. it is a genderless fluffy , witch makes it offically fluffy/kiara.

No one knows for sure. I know that the cub at the end of TLK 1 is a different coulour to Kiara in the second movie, but I believe that it was Kiara all along. Still, no one knows. It might have been.

No one knows for sure. These are all fan made stories. They were made due to Kopa being in Six New Adventures as son of Simba, which movie makers decided to change in female. But since both presentations, one at the end of TLK and one at beginning of TLK2 look different enough, and cubs look different too, many believe some time has passed between and that these two are not same cubs. Also no one knows why exactly Zira got exiled. I mean sure it is obvious that she loved Scar, but still some say there must be some more to her exile, then just love. So fans made stories about Kopa being killed by her to cover all these questions and connect stories into something that makes more sense. Another version is about him escaping and running away, similar to what Simba did. His return is again subject to individual story.

But do note that is not official. It is fan made. Disney did not say anything about Kopa, only thing Disney did state is that cub at the end of TLK is suppose to be Kiara. But some of us do have doubts. Which story you want to believe in is up to you. Fans are on both sides, some believing in Kopa and some saying he is not any more part of TLK universe than any other fan character.