soon
Why do you not believe there are parties that could amalgamate to challenge Labour if Corbyn doesn't win?
If Corbyn doesn't get elected as Labour Leader then those who see him as the right man for the job have decisions to make as to where Labour will be heading for them to continue being Labour supporters. After all they are mostly saying that Labour does not hold any conviction for them any longer, hasn't done so for a while, or so it would seem.
Corbyn has been a left of center MP all his life. His profile and values have been so prominent since the Leadership contest he will find it difficult to return to being a back bench MP probably. Why? Because whilst he has been a known name to those in the media and public who enjoy 'Westminster Bubble' watching , or watching him on Russia Today News, listening to him at meetings etc. Corbyn has been an unknown name for most of the electorate and they only have a limited knowledge of him but they like what they see and hear.
The fact is he is preaching to the converted to those who belong to or agree with parties such as Left Unity, The Peoples Assemble Against Austerity, Communist Party etc. If he fails to obtain the leadership why wouldn't they try to get Corbyn to be a 'front man' for a new left wing party where they all share a common agreement with each other. His profile now makes him an obvious choice and his age might just make him think it's now or never if he fails to get the backing for Labour Leader.