Let's ask @kspence92 what is the official canon regarding the status of NI joining ROI.The UK is definitely still alive but just ignore the fact that the UK is also kinda in a "civil war" or something against a certain "Federation of Great Britain" after Northern Ireland at some point of time between 2003 and 2012 voted to join the Republic of Ireland.
It's unknown how internationally recognised the Federation of Britain is as opposed to the rements of the UK and monarchy.
Although the F.G.B. seems to get forgotten about a lot in this thread since the post discussing it and the unification of Ireland wasn't threadmarked.
Actually a substantial amount of story driven posts by the OP in this thread were not threadmarked, but most of them had reasons for not getting marked.
I'm surprised too Scotland did not declare independence when it could have easily had. In one chapter, Scotland chose to remain loyal to the Belfast provisional capital of the United Kingdom.
The FGB is just a loose confederation of NATO repatriation cities. They don't actually share borders with each other. Trade with these cities travels through abandoned highways, towns, and cities. The FGB seems to be only a temporary country until it could reunify with the UK.