It had >0% chance of being passed. It might have been small, but it wasn't zero. There is however, 0% chance of forcing a no-deal-preventing election now. Personally, I think if you have only one chance to stop a no-deal, however small, you take it... unless, of course, you're not actually that...
The problem is that it's already too late. If Labour called a motion of no-confidence on the very first day back from summer recess, the timeline means the resulting election would still be after Brexit day. Boris's first day as PM was Corbyn's one and only opportunity to try to force a...