Wherever the UK citizens choose to, just like it's up to EU citizens whether they want to buy from the UK. We have a global market, (for the most part) anyone can buy anything from anyone else. The UK is likely to experience price rises for EU goods, and the EU is likely to experience price rises for UK goods, but if customers still want a particular product and can afford it even with the price rise then they'll continue to buy it.

> "Apparently the pound just fell to a century-wide low..."

That's just the markets reacting to uncertainty. The future is indeed more uncertain, so it's to be expected, but uncertainty does not necessarily mean a downturn in the long run.