[embee]

Without throwing brick-bats, I think Corbyn has shot himself in the foot with his stance on not joining in with discussions. Whether May does or does not take anything off the table, and as said in her letter neither she nor the government can stop no-deal, only parliament can do that, discussion really is the only way forward from where we are now. Whatever May comes up with in the next few days or next couple of weeks, parliament will have to approve what we go with so Corbyn's red lines are completely irrelevant.
We are in binary choice territory. Either we come up with a proposal or we don't. No proposal means either no-deal exit or revoke art50, that's it. A proposal means maybe the EU will consider an extension of art50 to allow enough time to pass it through parliament and agree it with the other 27. That's a big ask by anyone's standards but it's the only real alternative option, and it would have to be an almost foregone conclusion before the EU would agree to it.
I'm still not sure what the majority opinion of the Brexit voters is. Whatever outcome we end up with, I suspect the majority of the UK population will not be happy.
On balance of probability, I suspect we will leave with no-deal. If we revoked art50 the UK would have lost all international credibility and possibly risk civil unrest at home. I know it's only my opinion, but this is a case of the worst outcome being the only viable one. One thing we can be sure of is that whatever the outcome it will be blamed on the EU.