Problem is though that the Scotland/England comparison doesn't really work in that regard. The SNP already had a much more solid base in Scotland than UKIP did in the north of England. UKIP hadn't come close to winning a single seat; the SNP had basically already taken Glasgow at Holyrood in 2011, and had pretty much been making steady gains on Labour for the most part of a decade. Indyref gave them the catalyst to go on and annihilate Labour in 2015, yes, but Labour's problems up here ran a lot deeper than that, and 2015 would've probably gone poorly for them no matter what. Indeed, while it's something I'd probably need to see data to verify, I suspect the SNP would've done a lot better up here had Labour not been led by Brown, who was more well-liked up in Scotland for obvious reasons than down south.
Had Corbyn hypothetically gone full-blown Remainer, his popularity would've potentially been dented a bit in the north, but not to the point where it'd have actually cost him seats he already had a 30% advantage on. Especially considering UKIP collapsed, and the Tories remain toxic in such areas. These areas voted Leave, sure, but many of them narrowly voted Leave - if there's a 45% Remain vote in said area, and most of those Remainers want to vote for you, then you've basically got the seat in the bag provided it's not an absolute two-horse race.
Most of Labour's voter demographic was primarily voting Remain in the Brexit referendum. But indyref saw key Labour areas/voter demographics opt for a Yes vote (Glasgow, young people etc). The two cases were quite different.