I read somewhere that it would take a decade to unravel and pick apart the end of the Monarchy. It would take legislation by Parliament and the Monarch her/himself signing that legislation.
It will be a long, slow painful process if ever anything were to happen and it won't be in my lifetime, nor my kids.
Barbados, I feel, has set a precedent for pulling out the C/wealth and there will be more, and those that stay will question whether that is the right thing. There was no referendum for Barbados, the Government just decided, and I never saw any opposition to that.
There's 15 countries with the Queen as Head of State, it's beyond me why the likes of Canada, New Zealand and Australia would want to continue that after the Queen dies. Jamaica too, and I think they are on the way to do what Barbados has done.
I have linked this before, and forgive me if you have read it, but it's fascinating. (I am just filling in time waiting for that flippin' verdict on PA's case)
www.businessinsider.com/what-happens-when-queen-elizabeth-ii-dies-king-charles-2018-6?r=US&IR=T
QE dying will be the most disruptive event for 70 years and will cost us billions, the article goes through it all.