The choice of PM is not up to the oppostion(s) to decide really.
The opposition(s) can shout from afar but that is all they can do, if they want to install their own PM they have to win the election first. Which I think will not happen for at least 3 terms.
PM May is doing just fine but as usual she has to deal with many obstacles thrown at her, which is rather normal in British politics really. 😀
In my view Corbyn should remain opposition leader for at least 3 terms.
Alternatively, the opposition might want to have Emily Thornberry as their replacement leader.
Emily Thornberry the new Labour leader perhaps? 😀