If this government fails why would anyone still consider a vote for Corbyn? The man for a start intends to ruin and alienate anyone who enjoys making money, in a capitalist culture and society that for a start is political suicide. It is a common misconception that the vast majority in this country are either far left or right. The centre is the vote that always wins elections where no real outright winner can be seen, the lack of leadership from the Tory's was the reason Blair was so successful, the tables have now turned and Labour need leadership not radical ideas.
A lurch to the extreme left will gather many votes from the left and also those who are now showing sympathy to those in plight but certainly they will change their minds when such a radical change will be at your own expense. Ultimately Corbyn alienates the other 80% of the population and even a lot of MP's in his party who don't want socialism but rather just something normal. He may well win the Labour election and fair enough if he wins but remember he has only gathered support from a % of Labour voters, not the rest of the voting public.
Personally I believe the Tory's will have a field day if Corbyn gets in because they can so easily dismantle his policies which are at the moment based upon the same facts and logic told by a local drunk in the pub. The only real danger is the transition the Tory's will have when it comes to changing leader but even then whoever they pick will probably end up the sane option compared to Corbyn.