The worst case scenario for Labour would be for both fragments of the Labour Party to be largely wiped out at the next general election. Perhaps the 50 or so SNP MPs would be the official opposition in the next Parliament, with a very large Conservative majority and other anti Tory groups reduced to small fragments which would have to realign into something new to create a credible future challenger for government.
If something like that were the case in extremis, than I can see a lot of those Yorkshire-style "hard Labour" seats going UKIP rather than Tory--sort of like, UKIP being to SNP what Reform was to the BQ in Canada in 1993...
