If anything the property market in London will probably go higher if it is seen as a desirable but firewalled from EU location. There is every chance the UK will become a Switzerland - a place to do business in Europe, but relatively safe from the poorly run economies of Europe now that seem to have been on the brink of bankruptcy for a decade or more.
The decision has been made - the next decisions have to be around creating a USP for the UK as an ideal place of investment. It's an ideal time to introduce things that benefit the startup sector, including Fintech startups by making it easier to avoid the red tape of Europe while tapping into one of the worlds biggest financial sectors.