Corbyn is done, if not tomorrow then soon. The main reason for that is that he is basically a lib-dem in labour clothing. His stances on many issues from environment, to nuclear weapons or human rights are admirable, i personally support many of them. But that's not something that worries typical labour voter, especially in the last couple of years. And no matter how hard Corbyn tries to go from this "Kumbayah" image it simply does not work for him. He basically lost the core of the voters in England to UKIP and even Tories, who successfully took pages out of UKIPs playbook without any racist and etc fallout.
It's a sad situation, but when Corbyn talks about Tridents most of people disillusioned with austerity and recent UK recovery, so basically an opposition voters, are like WTF, i don't get it all, what's a Trident anyway?
The only thing that could have saved him actually if he would have basically abandon most of his principles and convictions and became the leader Labour needed, not the one he actually is and always was. But he thought it to be his chance to finally explain and convey his sometimes radical or unusual but in a way smart and creative ideas to general public, to make them believe in this fairer, peaceful, more productive society he always envisioned. But that's always was an uphill battle, especially in this climate. So all he did is actually alienate many of traditional Labour support, that went to parties with much more simple and down-to-earth agendas like UKIP or SNP. Their messages are like one sentence and everybody gets them.
Corbyn was in a way brave, honest and faithful (to his principles) but ultimately stupid.