1. NI won't leave: the underlying issues that caused decades of bloodshed are still there, and this'd cause a
massive resurgence... only this time, there'll be more attacks on RoI soil, too.
2. A certain Scottish politician is massively overrated, as is the support she boasts from "fellow Scots".
Most Scottish people don't want to leave the UK because they recognize how fucking stupid an idea it is.
Scotland has no real infrastructure to generate independent revenue to support an entire country. All the oil-fields, for example?
They belong to Westminster.
Ironically, most of the jobs up there come from Royal Navy and military-related professions -- that includes the support jobs, up to and including catering and ship-building.
All the neat little perks the Scots get, like free university and the NHS subsidies? They'd all vanish.
There would be no 'retroactively' remaining part of or joining the EU. Hell, Scotland on its own doesn't meet any of the criteria to even
apply for membership!
If anything, a more realistic scenario would be
Cornwall being recognized as its own country and part of the UK than Scotland leaving.