When does the United Kingdom become the 51st State, bow to the FAA and adhere to FARs?
I think it's going to be renamed to "Airstrip One".
I doubt that EASA was discussed.
I very much doubt that too. "You see, Nicolas, this 50 Billion contribution of ours to the stability fund is not really a problem, but I'd like to talk to you about this Cologne Agency..."
Will this lead to the UK being expelled or voluntarily leave the EU?
No it won't. There is a difference between not buying into something that would be truly detrimental to the UK (and which any sensible UK PM would refuse to do) and leaving the Union (which I think would really be detrimental to UK).