Brexit was messy not because such possibility did not exist, it actually did - UK triggered exit article and there was some procedure for it. The problem was th

Brexit was messy not because such possibility did not exist, it actually did - UK triggered exit article and there was some procedure for it. The problem was that it is impossible to have a rollback or a national fallback for every EU regulation, neither UK wanted to have such fallback in all cases: they negotiated to cherry-pick the regulations they liked, while abandoning the others.