The EU specialises in arguing based on fatuous and misleading analogies. We used to be told the UK had to stay in the convoy, an unfortunate image given twentieth century European history. Then we were told we must not miss the train, though many of us did not want to take a train to Brussels Central to be told what to do. Now we are told we will fall off the cliff if we just leave.
There is no cliff or cliff edge. There are numerous deals, contracts and joint activities which will continue after exit as before.People and businesses from Non EU member states fly to the EU, buy and sell with people in the EU, undertake joint ventures with the EU, come to EU universities. So will we once we have left.
I have still to hear from another member state what barriers they wish to impose on their citizens trading and travelling to the UK. It is difficult to see why they would want to get in the way, but if they do the WTO and other international laws and treaties will stop them doing damage to us.