Never mind Scotland having another vote as to whether they stay in or not. Turn the tables, lets have an England, Wales and NI vote as to whether we kick them out. I can guarantee they'd hate that but it would play into SNP hands perfectly, the Evil English booting us out of the UK blah blah blah.
Let them run their own country for a few months, there'd be a hell of a lot of immigration that year.
Grab a map, immigration wouldn't be a problem for Scotland as the main border for it is controlled by the French into the south of England. Not many will manage to get through those waters all the way up to Scotland as there simply isn't the boats for it, so their only option is to come via England.
Apart from anything else England, Wales and NI would vote to keep Scotland in, there's far too many benefits of doing so, as much as you may want to say otherwise. Outside of London there are precious free regions which contribute to the treasury, Scotland is one of those, vast swathes of England do not, NI certainly doesn't.