You may be right, they've already done it with Miliband, then gone further left with this bloke, both with disastrous
consequences although, other than McDonnell, I don't know who'd fit such a bill.
If they do go down that route, then it really is game up.
Your idea of disastrous consequences are probably very different to Corbyn's. He will consider himself a success if he moves the party permanently further left, removes the Blairites. He's naturally a poltician who favours opposition so wouldnt judge himself on how well Labour perform in elections.