When that happens, I thought Corbyn is almost certainly expected to call a VONC, thereby triggering a general election.
Corbyn will never vote for a GE he knows he will lose. If there was a GE this winter, the Tories will walk it with a good majority, thus also removing the power of the DUP, so the DUP won't want a GE either.
At the end of the day, Parliament has no choice but to vote for the deal and then the opposition parties can get their ducks in a row ready for the next GE (i.e. Corbyn can be replaced with someone who is electable). The politicians don't want another GE until Brexit is resolved as it will just tear them apart even more.