Maybe Kovu? Well, it is known Scar chose him to be his heir, and when Scar dies and Zira loses access to Pride Rock, she brainwashes him to kill Simba, and become the king. But, it is never really known if Kovu personally wanted the throne to begin with.
Maybe Vitani? Siblings of a royal heir can have the throne if their sibling doesn't produce a successor, like if Mufasa died not having Simba as his heir, then, Scar becomes king. However, the movie didn't tell us much of Vitani or what's her personality, but I guess she doesn't want the throne, and is happy enough to be a Pridelander.
So, who will be Simba's successor based on those assumptions? Unless Simba and Nala have a son?
