The British have many more precious things that that.
They also have a rule of law determined by the BRITISH (NOT Brussels), responsive and accountable government (even though of course trade offs must always be made), and still have enthusiastic citizens from around the world banging at the door wanting to get in. As well as a dynamic and capable population of natives willing to bear the costs and risks of really changing their society in the 21st century. And they are still a welcoming society, them feeling they are in control again will make them more welcoming, not less.
People counting out the UK yet are being very premature. There will certainly be economic pain from this and likely other costs, but there are potential big benefits too. Brexit is a story that will play out over the next 10-20-50-100 years, not just the next 5-10. Would not surprise me at all to find the UK a wealthy more developed nation than Germany by 2050.
Even when you look at the Boris Johnson Cabinet, the ideas and intent that is emanating from there is very promising. No more "we can't do this because Brussels" or "nothing can be done". Real thought into how to make the UK remain relevant in the 21st century on its own terms, real efforts into how to improve the country.
This isn't the End of History. This is the end of the insular old folks home the EU is at danger of becoming.