Cameron could survive a no confidence assassination if he keeps us in. Indeed, it would make sense to deploy BoJo later on, having had a more senior role in the cabinet arranged for him in the interim. He's not a great Commons peformer, so the fewer days to gaffe before a GE, the better. Then do a run off against an open field, possibly face a no-name moderate at the final ballot, head to the polls. BoJo is calculating enough to see the advantages in this. Hence why I've come round my summary point earlier.
Also the trade jig still just doesn't add up.
We would lose more money on tariffs and non-tariff costs of trade under Brexit than we currently spend on EU's membership fee (amounting to, as a neat figure: 6-10% of our trade receipts in goods and services with the bloc, or <1% of our GDP), whichever way you slice it, the new trade magic(tm) approach will wipe away any 'big savings on Brussels excesses', lol.
The mooted scenarios:
1) WTO->FTA->FTA-active
2) WTO->EEA
3) EEA->FTA->FTA-active; if allowed -- no precedent
4) EEA -- if not stupid and the EU agrees to waive the formality of us negotiatng back in under reduced association terms
Repeat 1 for up to 50 times with EU's current FTA partners, the Canada-esque option. We reciprocate, the volume of trade goes down further. Easily eats <1% of GDP in and of itself, Obsborne's projections notwithstanding, due to innefficiency of FTAs vs the single market alone, as Fox often hints.
Money thus expended is not spent on a membership fee with benefits attached, but gone down the pan; and that's without anyone 'spiting us' really. Talk about waste and reclamation. Most annoying for the financial rectitude crowd, I'm sure.