For someone who declares zero confidence in forecasts, you seem quite keen on them for some things like election results.

I have no real idea how long Johnson would last as PM. It could be a long time, definitely. On the other hand if he finds himself obliged to accept an extension beyond October, his support could disappear overnight. Even without that, if he leaves with no deal and a fraction of the claimed problems come to pass in say the first six months, again he could find his support becomes thin.

For what it is worth, I am not with those who think everything will collapse the day after a no deal. It will take several months for the more serious issues to hit, though there could be a goodly number of problems in the first days or weeks. Providing we don't have severe food shortages or similar, any immediate problems will be dismissed as "teething troubles."