Sorry if this was already posted, but here's something Sakurai said once about story in video games.
Quote:In games where you're fighting against enemies, you're playing from the perspective of the hero, and you're being asked to basically win every time. If players wind up in a predicament because of what the story calls for, that's like penalizing them even though they made no mistake.
I can't find/remember the whole thing, but I think he was referring specifically to RPG plots killing off party members you invested time into grinding, getting weapons for, etc.
I don't think any Skylander should die for the sake of adding "maturity" to the story.
From a gameplay perspective,
it would be punishing and frustrating for players that aren't interested in the story and just enjoy the gameplay, it would make people lose their favourites, and from a story perspective it doesn't even make complete sense because the Skylanders are supposed to be frozen on Earth. Now how that affects their mortality is a mystery, but since they're supposed to have a tangiable form in real life, I don't think the plot of the main games should affect their usability.
Then again, that whole "Portal Master summoning frozen heroes" idea has been in shambles since SF and was even falling apart during Giants. Heck, even in SA it was inconsistent at times. Anyway, at this point, I would be surprised if there is an official explanation for why the vehicles are on Earth.
Either way, it shouldn't happen, because gameplay.