At some stage in any deal, negotiations come to an end, the EU leaders have ratified this deal, if it is rejected, are they going to go back and change it. Probably not, they will say no, because any new deal is likely to be rejected by parliament as well.
The Tories will go for a plan B and play for time, then they will all go home for Christmas. In the New Year there will be a vote of no confidence, will there be a GE?, maybe but not until mid February at least. Then even if JC wins it is highly likely that the SNP will hold the balance of power in parliament.
A second vote???. Would it give a different result???. It might make it worse and make no deal inevitable MPs would not welcome that
Maybe just maybe parliament will vote to stop Brexit, because I don't think there is an apetite for no deal. And TM stays