Switzerland and Norway come to mind as countries that rejected being part of the EU, and they are doing well for themselves without the heavy hand of Brussels.
The UK could be equally if not more prosperous because of their trade with the US.
“Our main focus has been getting those trade agreements that the EU already has with third countries; to be in a position to be able to either roll over if there is no deal, or to be able to be in a position where we can build upon them if there is an implementation period,” Fox explained. “That process has gone well, we’ve got some differing approaches with different countries to make that happen.”
https://www.oann.com/u-k-trade-secretary-london-preparing-for-no-deal-with-eu-on-brexit/