Uh they're not actually sisters as far as I'm aware that's just kayfabenot sure about the new guys but want to put my cents in anyway.
If they actually lose Selen that's gonna lose Elira too they are literal sisters and I find it hard to believe one finds ninji's tardism fine while the other walks.
Elira dispite the "clique" Rrats being semi jokes will at bare minimum having older talents reevaluating their contracts they lost Elira we might as well consider Ninji a dead corpo in EN.
Elira leaving might also prompt Millie and Enna to also walk especially without Nina there which i suspect would make Reimu walk as well. as holding a generation wave by yourself is a mental hell i wouldn't wish on anyone.