Not really. A main protagonist would be someone who appeared longer than 5-10 minutes. Such as Pumba, Timone, Simba, and I think Nala. Mufasa died in the beginning of the movie, so he doesn't really count as a main protagonist.
Mufasa was in the movie more than just the beginning. He was in Simba's "visions." Either way I think it's obvious that there have been deaths in Kingdom Hearts already so theres no reason there can't be more.