I agree with much of what you said, but not this bit. The UK consisted of two countries (England and Scotland), one province (N Ireland), and one Principality (Wales). In theory, equal partners, but in practice not. Northern Ireland would never seek independence, and Wales would never be permitted to, or in practice want to, given the lack of any real size or economic clout. I think the secession of Yorkshire would cause Westminster more concern to be honest. It's already a world away, so how far do you want it to secede? Might have to make the furrow that is the Pennine Way, a bit deeper and wider.