Not quite right there - it is a requirement of EU membership that a country becomes a signatory of the ECHR...which, although slightly different, would still be used by Human Rights lawyers to enforce legislation similar to that which affected Mick's firm. Therefore it IS relevant to this discussion because on the face of it, the UK would have to leave the EU if it refused to comply....I bet they would soon back down if the UK called their bluff, though....
There's absolutely no way we'd be required to leave the EU if we repealed the Act and reverted to the domestic legislation, which is perfectly fine. As you say, they'd back down.