As someone who hasn't followed the politics of the British Isles closely, would it be possible for NI to leave the UK without Irish reunification? I.e. Northern Ireland would become an independent state. It would be a small state, but far from the smallest, and independence could allow a slow evolution over time from the status quo toward eventual reunification (or not).
In theory yes, but the only thing keeping NI economy from turning into Greece are transfer payments from the rest of the UK. Historically, there was also the small matter that the only thing keeping the place from descending into a civil f****** war was the presence of British Army and London government being there to intervene (indeed, ruling NI directly) in case the Unionist majority decided to go full on fascist. That might seem irrelevant today, but sectarian resentments plus an economy in the gutter is not a good combination.
This is the point people always seem to ignore. Unionists entire identity is about not being Irish, they will never accept being part of Ireland anymore than Sinn Fein supporters ever accepted being part of Britain. Unionist paramilitaries still have an awful lot of guns even post GFA..
The IRA were a piece of bad luck away from assassinating the British Prime Minister and that was with a military occupation and advanced intelligence service in the form of MI5. The Irish military/intelligence service is in no way equipped to deal with even a minor insurgence on par with present dissident republicans. And the unionists would have literally nothing to lose by fighting in this scenario, since they’d know there was zero chance of them ever going back to the UK.
People forget the Unionist paramilitaries were responsible for as much if not more violence than the IRA were during the 70s-80s, and they haven’t changed much.