It's not clear to me that the Brexit had to do with wealth as much as it had to do with sovereignty. It's also not clear that the Brexit will have a negative long run impact on Britain's wealth.
I know this sounds crazy to all the super smart international people out there, but A) the EU's growth sucks and B) it's likely to get worse before it gets better - oh, and C) when it gets worse the Euro could very well go away, making the Brexit crowd look like geniuses.
Look, if you look for fulfillment in money or possessions you are going to be disappointed. This has been a tenet of Western philosophy for millennia. Using this philosophy as a platform to trash the Brexit is disingenuous and beneath somebody as uber super smart as Hawking.