Technically no we haven't.
We have left the EU. We haven't left the ECHR.
The hard right of the Tories would like to do this next. Mainly because it would strip of us of the ability to uphold a bunch of rights as citizens. And would had power to big corporations and the state.
That said, if there is a ECHR ruling which we refuse to follow there's also limited repercussions if the government refuse to comply with it. EU member states could try and force us to comply by threatening with blocking other agreements or deals. But there's still a limited amount they can do if the UK government says "hmm nope, no thanks". Whether Starmer would have the balls to do that, I'm not sure but it is an option. He will be looking at Reform and the Tories who are lining up the ECHR in their cross hairs for the next election. Starmer gets to choose whether to play to their agenda or not in this scenario.
Further to that, other European countries will not all be wanting to touch this subject if they can possibly help it because they will be looking at the US and then back over their shoulders at their internal far right parties going "hmmm no maybe not. Maybe we'll just let this one slide and hope no one notices". Cos own self interest and an understanding of just how bad the optics on all of this are.
Cos politics.
I think the shark has been jumped with lady peni and pregnant men leading to a potential 'woke backlash' which is suddenly actually being taken seriously.
I hope it goes the way of women, because it's a lot less stressful and problematic in the long run, but I also think this ruling will ultimately have no good outcome for TRAs which ever way it falls.
The ship has sailed and is surrounded by those jumping sharks.