Don't forget Hunter and Blake's parents, the missing whereabouts of Jack and Z's parents, Sky's father, whose death is explicitly focused on, complete with a broken helmet as a "last memento;" and if you focus on mentors, technically Master Mao as well as Masters Guin, Lope, and Rilla were "ghosts."
Not to mention all the character's who "die" offscreen in heroic sacrifices such as Clare's mother and the rest of the Mystic Wizards, and, if you count them, the rest of Tyzonn's rescue team. And then there's the "almost deaths" like Isinia, Leanbow, possibly Daggeron, Vella, and, if they count, Masters Swoop, Finn, and Phant when they were sealed away.
The Disney seasons weren't adverse to death, fates worse than death, or having characters be/become "lost," or at least assumed to be the above, it all depends on how it's dealt with in regards to the story, such as the effect on the plot, character development, dignity and so on, and, in a particular case with Power Rangers, if it "stays" that way.
The "highschool dropout" bit doesn't sound too out of place, though it's a bit odd. In Shinkenger, Chiaki left his highschool just prior to graduation and by the end he went to begin his college entrance exams. If this is a kept character trait, I can see them adressing it similarly, if a bit lowkey, "Perry" 'left' school to take up his duties and then returns to it at the end, all without using the term "dropout" as it "might send a bad image to children".
