He doesn't expect, or want, to win. To quote his office from last week - they aren't looking to form an alternate government, they want to form a social uprising. He's literally preaching the failed politics of the 70s left.
Assuming they lose the election, he will stay on, and his supporters will blame labour Mps for undermining him and that they lost because people didn't understand his message enough.
It's literally the 80s come again. And, once again, labour will at some point grow the fuck up and realise winning elections is what counts before anything else. But until that point the membership will keep voting Corbyn in - after all, the majority of them aren't suffering from austerity anyway. White middle class liberals aren't exactly suffering under the bedroom tax, or in work poverty...