I’m seriously starting to fear that we’re going to crash out of the EU with no deal at all at this rate. Is that the most likely scenario now? Is there any chance that TM or a new leader could get an extension to Article 50 or is that just not possible?
Any leader at any time can revoke or extend A50, that's their confirmed prerogative. Whether they will or not is an entirely different question.
No deal did just get a lot more likely, yes, but everything depends on who the Tories put up as leader and what they want to do, what (if anything) the opposition (ha!) does about it, what the DUP does about it, and ultimately what gets through parliament.
Frankly, I don't see why a change in leadership would change anything much about this situation. May's deal is the only deal we're getting. We're still faced with that, no deal or no Brexit. This is far more about Tory infighting than political reality, sprinkled with a few unicorns the ERG think they can tame.
Let's not forget the hard-right Brexiteers are incensed that Ireland has had such a strong voice in these negotiations and a lot of this is gammony bluster and outrage. See Owen Patterson's 'we are the source of the English language' ridiculousness in his no confidence letter. The absolute hubris of it all.