It's not clear to me why a no-deal Brexit would necessarily damage Boris politically.
For starters it would make him absolutely secure in the party - 70% of members want no deal and if that YouGov poll is anything like accurate they consider the break up of the UK a price well worth paying.
Supporting it in a poll and supporting it after you had to sell you kids for medical experiments because your plant closed down are you're destitute are two quite different things. Sure, Blitz spirit and all that will ensure there is no revolution in the UK. But promising unicorns and delivering untamed nightmares* isn't the recepie for a long, healthy political career either.
Furthermore the poll we all know and love asked Tory party
members. There are only about 130 thousand of those, out of 46 million eligeble voters in the UK. The fact a clear majority of 130 thousand is of the opinion breaking up the UK and their prosperity is a price worth paying for Brexit does not mean a majority of voters is of the same opinion (and not "thinks") the same. I made a point about self-selection earlier, it is probable a statistically significant number of members left the Tories in disgust due to Brexit, skewing the numbers towards "Brexit, come what may". I see no justification to assume Tory party members hold the exact same opinions in the same proportions as their one hundred times larger voter base.
Meanwhile the Labour Party is in disarray with a leader who still seems to be pro-Brexit and very reluctant to change his mind. Nothing new there, he's been advocating the same policies on everything since the 1970s despite the world changing significantly in the meantime and recent reports on the BBC had him listening carefully to 25 MPs who were warning him not to consider Remain as a referendum option and ignore the 100+ who are asking for a second referendum. I couldn't vote for Labour in an upcoming General Election unless they change both their leader and their Brexit policy. Even if Labour changes leader, they need someone with a similar level of "brand awareness" as Boris and not some capable but boring nonentity.
Whenever the next election happens, I can see the Conservatives getting 30% to 35% of the vote due to a combination of party loyalists and people who have heard of Boris. Even with Corbyn at the helm, Labour will get 20% to 25% which leaves around 40% - 45% being split between the nationalist parties (who should expect to triumph), LibDems and Greens.
With a split like that, and the vagaries of the first past the post system, if the Conservatives managed 35%, they could easily get a majority of 100+. If the election takes place amid post no-deal Brexit turmoil, I could see the Conservative share of the vote being significantly higher because people will be frightened to hand over control of the country to Corbyn.
Corbyn is indeed a major part of the problem with Brexit, he always has been. Still, all these arguments about how he's pro-Brexit and refuses to change his mind only work until Brexit happens. If there is a no-deal Brexit he's still the alternative to a Tory no-deal Brexit, with selling off the NHS to US interests being the key boogeyman this time around. Even with your numbers that assume the Tory party base would vote alongside Tory party membership (unjustified, IMHO), if the conservatives are on low end of your estimate and Labour is at the high end a relatively slight shift from LibDem, Green and nationalists to Labour could see the latter be neck-and-neck with Tories at least, perhaps forming a coalition with some to "manage Tory Brexit".
Plus of course - the next election isn't the end of history either. Even if BJ wins he'll be presiding over a mother of all recessions, an evisceration of the remaining British manufacturing, probably losing a few bits of country in the process all the while being rightfully blamed for it all.
Diehard party loyalists would still vote for him, sure. All 15% of the electorate. The rest would either stay at home or vote for someone else. I'm not sure he sees that far or indeed that he cares, but his place in history would be more along the lines of John I than anyone else.
McHrozni
*a dragon-horse with an attitude and a taste for human flesh