What group is it going to belong to, if it isn't part of the EU?
Why should we be part of a larger "group"? I see no reason why we should be.
It is going to take some work allrigh. There are tonnes of trade agreements to be re-negotiated. They need to arrange much stricter border-checks on visitors, etc, etc, etc.
But the European community are not the only people they deal with. There is the British Commonwealth composed of former British colonies. On paper it is led by Britain, in reality it is constant negotiations where Britain is not the boss at all. It has been there all the time from long before the European Union was even concieved and it is as chaotic as the EU ever was. They have the skilled people to handle that, so they are not really lost and alone now.
IMHO the situation is worse for the European Union. It might even fall apart now Britain is leaving.
I've always seen the US as a group unto itself. Its name says it all... the United States. :)
I don't know much about how trade partners' agreements work, I would have to discuss that with people who are directly involved in it and I don't personally know anyone who is.
I hear they are going to align with California after it succeeds.
It does not need to belong to any group... Switzerland does not belong to any group and it has one of the most prosperous economies in the world..