User blog comment:Xilinoc/Ch. 604 - REVITALIZE/@comment-4115054-20141109074008/@comment-5398287-20141109170723

That would be the logical course of action, but it would also mean no one else would get to fight and the second invasion would be over before it started. It's the same reason why Yamamoto had to get killed off early in the arc; if he stuck around, he could have very easily taken out every Sternritter and thus stopped the arc in its track, which he was fully intending to do after killing Yhwach.