Biggest elephant in the room of that direction of travel is Joe Biden.
Well, yes.
This government won't formally withdraw from the GFA.
I think they'll just simply begin to ignore the Irish Sea border. The EU will then either accept there isn't a border between the UK and EU without a formal agreement (which I can't imagine them doing) or impose a border between NI and the Republic of Ireland, which would play into the hands of this corrupt Tory regime.
If the latter, I would hope Biden has the fortitude to openly blame the UK for the collapse of the GFA.
There has only ever been 3 possible solutions to the UK/Ireland border issue:
1) Impose the border between NI and The Republic. This destroys the GFA, which is an international treaty in which the US is heavily invested (and the current President especially supportive of)
2) Put the border in the Irish Sea. This is the option this government has chosen, but the compliant media haven't made much of this fact, and most Brexwits don't seem to realise the formal arrangement exists. Potentially makes the possibility of a united Ireland more likely (I'd fucking love it!)
3) Reach an agreement with the EU for there to be no border. This would need the UK to accept a Customs Union and Single Market arrangement, with oversight by the European Court. This is unacceptable for those pulling the strings of the Tory Party - those with huge financial interest in ATAD/AMLD not being fully implemented in the UK, which would open up the BOTs and CDs for scrutiny by authorities and investigators.