I mean, Riho's for sure gone, but I feel like most of the formation change was just that the dance team is in a V instead of whatever-the-hell you call that shape they had been in before, and the dance fight was changed into a threesome instead of two one-on-ones. But I still don't see where Sakura filled in.
You can see it here, Sakura stepped into the position Riho would be in while her usually position would be where Zukki was, making the formation a little less off center. Yall are so semantical.
This performance made me realize MM doesn't rely on their ace to perform well together. It's real teamwork. They can hold their own. It must be because MM is so well balanced.
I remember J=J members realizing they had to step up their game when Karin was sick. It really made it obvious J=J was built around Karin. MM is a fluctuating group so they can't afford to rely on one person.
The group "needs" no individual. Doesn't mean Riho doesn't contribute though each girl does, and each girl is important. Each member changes the group in their own way. MM has always been about teamwork though, and that's what I took away from this performance, much like Mixi.