From what I read, within the UK is fine because UK law will still be governing everything.
For UK insurers, maybe.
However, we live in a complex world. Just take any individual aircraft. Every single component on that aircraft has to be covered by an insurance policy somehow. Not all of those policies will be underwritten by UK insurers. And the non-UK insurers will be bound by the laws of their countries - not the UK.
If even a single rivet or bolt becomes uninsured, then who would risk moving - let alone flying - that aircraft ?
At least we are finally getting to the meat of Brexit ... which is that the past 45 years have seen changes beyond the capability of any single country to absorb. And the consequences of leaving that complexity - or trying to re-engage with it on our own terms - are not simple.
For the few that like facts, there are worst ways to spend an hour than watching this programme about the evolution of air safety
www.bbc.co.uk/programmes/b03d690n
Notice how behind the technology there is a fuckload of paperwork, and alphabet agencies. As well as the by now not-needed and useless experts.
After watching that, who would you rather cleared your plane for takeoff ? The properly accredited and instantiated body. Or Jacob Rees Mogg (on the ground, of course) saying "just take off you traitorous bastards. Everything will be alright. Honest." ????????