One event I've noted that I think has been given less significance than it deserves is May's meeting with Merkel shortly before she revealed her plans at Chequers. I suspect she must have received some positive encouragement from Merkel then for her to carry on. I'm not suggesting this amounts to actual agreement, or that Merkel and the EU won't want shedloads of alterations and concessions to it, perhaps unacceptably so, but I do think it hints that a deal may be possible, which I thought not before. The subsequent government resignations back this up as well, I don't think Boris and the others would have been so quick to go if they thought her plans were definitely doomed from the start.
Whether she can carry parliament or stay as leader is a whole different matter though. The Tory brexiteers have always struck me as a particularly self-serving bunch, but the way they are now dripping out resignations indicates they may actually have some degree of organisation at last, surprising to me at any rate.