The SNP will not survive to the next Holyrood Election. There will be no devolution referendum (not least because only Westminster can legislate for one, which it will never do), so the fundamentalist wing will either break away or stage a ruinous leadership contest with the same eventual effect.
But what if there were such a referendum, and a Yes vote? No British Government would ever sign up to Scottish independence without at least a permanent 50/50 split in oil and gas revenue, if not a split per head of population. No Spanish or Belgian Prime Minister would ever permit the accession to the EU of a secession from an existing member-state.
But most of all, unless there had somehow been obtained a clear majority Yes vote in each and every one of Scotland's (all unitary) municipalities, then no Westminster Parliament would ever do other than follow the Irish precedent and legislate for the independence only of those municipalities where the majority of registered voters had voted Yes, with the rest remaining the Scottish part of the United Kingdom as already existing.
In other words, the Union is the only way to preserve Scotland, as such, at all.