Something which can happen is that in the UK, constitutionally, the next government cannot be forced to continue the process of legislating something which the previous government enacted.
Should Scotland become independent, the Tories would HAVE to respect the outcome. However, in the middle of negotiations there is a general election. If Labour become the incumbents, then they could completely legally cancel independence, and there would be nothing that anybody could do about that.
However, in the event of Scottish independence, it is very unlikely that labour could possibly be elected.