I agree with much of that.
I don’t know why people think that the Leave threat to the northern labour vote is equivalent to the remain threat to the southern Tory vote. My reading of the referendum result is that a lot of labour voting working class people voted leave as a great big fuck off to those who they saw as being responsible for the fact that their lives were shit - Cameron and Osborne in particular. If there was another referendum I would imagine a large number would vote the same way again. In a general election this November, however, their lives will still be just as shit, but I doubt many see leaving the EU as the pathway to the sunlit uplands. I suspect more see more value in voting the way they have always voted.
In the south, very few people people voted to remain out of deep love for the EU project. It was all about economics. I suspect in general people in the south will have a lot more to lose from a no deal exit than people in the north simply because of the way wealth tends to be spread (well, not spread) in this country. For that reason, I suspect a much larger number of remain tories will defect to the Lib Dem’s. Labour will not pick up remain votes in the south any more than Johnson will pick up Leave votes in the north. Like you, I imagine that the 21 ex tories will not be opposed by the Lib Dems and will largely be returned as independents to the same constituencies.
When push comes to shove, in other words, more working class leave voters will come home to labour in a general election than middle class remain voters will go home to the tories.
For all these reasons, I can imagine that post a general election the numbers in Parliament would not be too different to the way they look now - the tories being the single largest party but 30/40 seats short of a majority.
What happens next depends upon what kind of national unity program the rebel alliance can put together as a way out of this mess.