I think you are spot on - to even be considered to be allowed to re-join we would have to demonstrate it would not be anther 10 - 20 - 40 year run just to rip it all and ourselves apart again. However the pound thing isn't quite right - you have to declare that one day you are looking to adopt the Euro - whilst it need not be a pre-requisite for joining I also think its likely they would make an exception for us and make it a condition of joining.
Which European countries still use their own currency?
As Croatia becomes the 20th EU nation to adopt the euro, there are still a number of members that haven’t taken this step.
In total, seven EU countries don’t use the euro: Bulgaria, Czech Republic, Denmark, Hungary, Poland, Romania, and Sweden.
In these countries, visitors from the eurozone still need to exchange money before they travel. Here’s a list of the currencies they use and some more information about these non-eurozone EU member states.