The rise of online shopping has changed the landscape but it's not responsible for the shops leaving, that's happening because the property markets aren't flexible enough, they're not reflecting the change in value. They're acting as though shops are still the shops of the 1950s. The shops shouldn't be leaving, they should be worth less but staying put. You can't replace shops with online shops for all types of shopping, both have strengths and weaknesses but they're not perfectly aligned/complementary.
As for the pound, the drop wasn't caused by Brexit, it was caused by the decision to go ahead with Brexit, that's quite a different thing. The export situation would be good if it wasn't the case that most of our physical (and quite a few that aren't) exports are assembled from stuff bought at dollar prices, which more than reverses the benefits.