Well if he has given up on remoaners (not me I hasten to add, I voted to stay) he is going lose the next election for sure. We might be in the majority overall, but that won't decide the next election unless something extraordinary happens. He might win back a lot of the green votes, but the Red Wall will still collapse, because that is where the Brexit voters are and there are more than sufficient amongst the remoaners who are never going to vote Labour again now to make sure Labour loses.
If Labour and the Conservative parties want to hang on to some semblance of power, they need unite and reform the voting system to some form of PR. They will probably never win an outright majority again then, but they will still stand a good chance of being the largest parties. We haven't had a government that has got over 50% of the vote share since the early 1950's if you exclude the Conservative/Lib Dem one. That cannot be good for