Talk of getting out of the WA is not new; in March 2019, the Commons Lib explored whether the UK would have any grounds for termination (in whole or in part, eg, Protocol only).

Its findings then remain relevant today: https://commonslibrary.parliament.uk/research-briefings/cbp-8463/

To summarise: time having passed, and the UK now realizing that it's not keen on having directly effective EU law in NI (and, re state aid, the UK at large) forever, are not changes in circumstances under Art 62 VCLT. They are regrets. That's not cause for termination.

Where does the debate about breach v termination go? Depends on what's being breached, as set out in WA. Joint Committee + arbitration with CJEU interpretation, *or* the CJEU outright, if UK actions amount to a violation of EU law still applicable to the UK under WA.

If no resolution there (eg, losing party fails to comply with ruling), the law suggests part of the WA will then be punitively suspended by the winner and penalties may arise. Can't suspend Part 2 or the Protocol, though, and so if breached, I believe they would limp on unevenly.

Would this kind of breach harm the UK's reputation? Sure, but it's not clear what the practical consequences to that would be. Border on island of Ireland? Maybe. But then everyone loses, including the legally "in the right" EU. Not much of an outcome.

This thread is going to fizzle out here. International law works because, like money and time, we generally agree to pretend it's real and meaningful. When that stops, all my knowledge about international law is about as helpful as my knowledge of the Taylor Swift catalogue.