User blog comment:Neetaku/Grisha Yeager is Alive/@comment-27441457-20160103031515

I don't think the Reiss rituals have to involve the Coordinate wielder being COMPLETELY consumed. When we're shown Frieda eating Uri, it seems she only bothers to eat his head and upper torso, leaving his lower body and arms. We haven't yet been told the extent of what regeneration can regenerate, so I'm assuming that much is enough to kill a Shifter.

And it doesn't make sense for something to regenerate if it isn't connected to the brain. Eren's missing arm hasn't regenerated a second Eren.