What about this madcap scenario? : Rather than let her bill fail, she makes a speech which says that her government has decided to remain, in the interests of the country etc. Public uproar but less than 50%? . Corbyn calls a GE but then what? Tories are remain and what can Corbyn do? If he switches to remain too (which he would likely have to do) he is no better a hypocrite than May but if he says he will respect the public vote (unlike May blah bah blah) and is committed to Brexit it will become a GE which he fights on an "integrity" level but is effectively a referendum /second vote. May will have to go of course but the Tories remain in power if she plays the hand this way. Interesting slogans on buses and a voting public confused as f**k! Sometimes you have to bluff with a 2-7 to get the Aces to fold. Very handy timing for Alex Salmond too...
If May was now to switch to just staying in the EU out of the blue, it could well cause the Tories to break up. Although I wouldn't put anything past her or Corbyn for that matter, as both want power for power's sake regardless of the fallout as this Brexit process has demonstrated.