Elekible- Maybe in your opinion but I like for Emma to get some more storylines and could stay in the show. We could also do without Beiste, the principal, Brittany and a quite few others to be honest (Okay no Glee couldn't survive without Brittany, she's pretty much the more funniest one there).
The show could also survive without Finn, infact everyone but Finn, Rachel, Blaine and Kurt might as well be filler characters, wouldn't be surprised if the writers though only they could take it. And even then Finn/Blaine are only getting screentime due to the fact they are dating the core two.
S1 dealt with many of the characters fine, although Tina, Santana and Brittany could have been worked on a little harder. (And at that time Mike was more of a filler character then anything)
Well all those main ones you mention are graduating, Finn, Rachel and Kurt were confirmed, and considering Blaine is Kurt's age, he must be graduating too.