Both options, Leave or Stay are a step into the unknown. I am saying that you can't predict what will happen if we leave, you can guess but that is all. Your forecast is no more certain than any other prediction.
My guess is that we can maintain a friendly and peaceful relationship with Europe whilst selling to the countries which want our goods and services. Similarly, we can buy goods from those countries which offer something appealing to us. That has happened since the beginning of time and it will continue with or without the EU, history is on our side.
The EU stance seems to indicate that friendship, cooperation and trade will be stamped out, extinguished and not be allowed to flourish unless we surrender increasing amounts of our independence to this faceless system which no one seems to identify with. It does not have to be like that, we can be friends with the EU after Brexit. Of course, if another EU nation repays our friendship and help with acts of open hostility and aggression in the form of an invasion (as seems to be prophesised by the IN Campaign), we have our Trident missile system with which to defend ourselves.