NI and Scotland aren't seceding.
Scotland had a referendum on that and chose to remain.
The SNP leader Sturgeon is like a hyperactive munchkin / oompa loompa hybrid. Like Mel Gibson in Braveheart but with a more ridiculous accent.
Basically wants referendums until gets result she wants....
Anyhoo, Scotland will be in trouble is they leave the UK. They do have North Sea oil - price of which has fallen and if they do leave, they won't retain 100% of it anyway. They, like Wales and England receive funding each year according to a Barnett formula - sadly, this is flawed meaning Scotland get more per head then Wales or England and disproportionately so. They'd lose that money.
Sturgeon's financial plans following independence already have gaping holes in terms of the funding - they'll be bankrupt within a year.
Plan to join the EU? Depends if they are wanted. Spain will object - they would be concerned abut their Catalan region wanting to up and leave also.
Assuming they get into the EU, they'll almost certainly have to ditch the pound sterling ( they seem to believe they can retain the UK currency if they secede ). That means harmonising with the Euro and, well, see Greece for the example of trying to homogenise disparate economies.
Scotland export 90% of trade to England. Want to leave the UK? Join the EU? Well, they'll lose freedom of travel, visas being required. They'll also have trade tariffs applied.
The problem in the Uk was the Remain camp want to simplify it to "whoever votes to leave is clearly racist". Which is ****. Controlled immigration via an Australian style model is what is needed; skilled workers in rather than unskilled.
The problem is that back in 1975 when the UK joined the European Community, it was established as purely a trading block. A European NAFTA. The problem is that over time it's become a creeping socialist experiment. Let's integrate politically. Let's have control over justice system. let's have a common currency. Unlike the USA, the political, economic, cultural and language differences are too vast and wide to have a "one size fits all approach".
The EU can issue things called "directives". These can apply to all nations or be targetted at specific nations. So, EU may pass a directive at Britain to say ensure all food produce is in pink and green coloured wrappers. ( Deliberately using a farcical example ).
Nations targetted by the directives are given the end result. They have freedom to implement laws to achieve that end result. However, they have to implement those rules to fulfill the directive. if they don't or have a poor law then the EU can refer that nation to the European Court of Justice.
It's a horrendously overly red taped undemocratic... thing.
Cameron renegotiated a deal. Within days, EU officials mocked the deal, European leaders mocked the deal, we were told "no further renegotiation". When the prime Minister had to try to sell the Remain vote to people, the Eu couldn't even throw him a bone, any form of sweetener.
If it had purely been kept as a trading block, I'd have agreed to vote Remain with reservations. What idiots at the EU want is a "United States of Europe"... which nobody in Europe really wants. EU have now lost the then 5th biggest world economy, 2nd biggest net contributor ( and I'm sure Germany will now be happy at having to subsidise everybody with little help ) and the largest military force in Europe.