I would think that if corbyn won, the last thing that would happen is another coup, simply because it would be utterly pointless. No one else in the party could beat him in a leadership election if he wins a general election.
For the polls, it is not just about 'shy tories' this time. There is another factor, probably bigger, and that is the youth vote. 2 million under 25s registered to vote after the election was announced, corbyn has a massive 60%+ of those voters, and ALL weighted polls you see balance against the young voters because historically they simply do not turn out on the day. That is, when they interview younger voters, they weigh their responses much less than any other age group.