Thing is, as I've said already, I actually kind of agree with him. I don't think the New Labour tendency (which - after all - forms the bulk of the Parliamentary Party) can exist within a Corbyn-led party. I watched him on Andrew Marr and came away puzzled (and quite heartened) by just how unashamedly left-wing he really is.
I'm not saying we can expect farm collectivisation to feature in the next Labour manifesto or anything, but he is a long way to the left of Blair and those that followed him. And I don't see them accepting his leadership.
At that point the only real question is whether the split comes in the form of a mass migration of MPs to the Lib Dems (who would probably welcome the colonisation and assimilation with open arms) - or whether they form an official "New Labour Party" - though the costs and logistics of that would far exceed the LibDem colonisation strategy.
What remains of Labour when the right jumps ship might not survive as a significant force in UK politics. Clearly I hope otherwise, but the risk is always there when a movement splits.
Corbyn impressed me more than I expected him to. Which makes me very pessimistic about his chances of mainstream success ;-)