While we don't know for sure, UK is a country of over 60 million people and a big player in world economy. Countries will continue to trade with UK, airlines will still want to fly into UK, especially Heathrow, the busiest international airport in the world, and UK consumers still want to buy imported goods. The worst that can happen is Brexit happens with no agreement and WTO tariff gets imposed, meaning imports may cost about 10% more - 10p on top of a bunch of bananas, £1,500 on the cost of a small family car. Not good but not disastrous. This will open up demand for UK-sourced goods, benefitting the domestic economy. In the long run, UK will conclude its own trade agreement worldwide, enhancing its standing in world commerce.