The only way this could possibly work is with a tight schedule of actions:
1. Secure an A50 extension
2. Conduct a 2nd Ref
3. Hold a GE
With a disparate alliance able to withdraw their support at any time (thus making the GNU fall), there would be no room for deviating from the schedule.
Problem is, I can't imagine Corbyn and his team going for anything like that - and the TIGgers are too intent on despising Corbyn and not losing their Parliamentary seats in a brought-forward GE to support it, so would likely vote against and risk a no-deal.