I'm pretty sure Regis is going to die, stories involving Kings and their old enough to rule sons tend to spell bad news for the kings. I can also see Lunafreya's bodyguard getting killed off for a character building moment for her. While I don't really see the main playable cast biting the bullet, I can totally see them pulling a fake out one where each member has to stay behind to fight something so Noctis can move on, with each scene looking absolutely dire for all of them until they all show up in a heroic rescue of Noctis at his lowest point in the final battle.