I didn't say they need to be kill off. Be gone, sure why not. Anyway, Logan/Older Xavier weee killed after 9 movies. If Erik and Raven get killed, they won't be a loss to the series especially when a lot of people are tired of seeing them again and again when the actual X-Men serve as wallpapers. Unless Fox fail to develop a good story for the others. Also, this will be their 7th non cameo role in the series, that's a big much when you consider the actual X-Men appearing in fewer movies and smaller roles.