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).
I’m pretty sure the Catholic majority border areas (Fermanagh, Tyrone, Derry City, South Armagh, South Down) would just jump ship to the RoI in that event leaving NI a rump state.