I think a large increase in the SNPs share of the vote (be it in an upcoming Scottish election or in a future general election) would be a precursor to a second referendum. At that point I think the result would sway in favour of independence. I can't see a referendum being granted by the UK government if the SNP fell in popularity.
Devolution at the very least is what an overwhelming majority of Scottish people want, so it isn't going anywhere anytime soon.