@mummmy2017
I think it's rational to think other countries would want to maintain their relationships with the UK. Agree.
But it's not so straightforward. If we take Korea as an example, I understand that cars have a particularly low tariff if the content is 55% EU ... So what happens to that 55% when the UK is selling cars to Korea.
And there are 295 of these agreements to 'copy-paste' as you say. The US has already begun to try it on and put a regulatory wedge (sanitary and phyto sanitary esp) between the UK and the EU. The US does not care about the UK save to make the EU's regulatory sphere of influence weaker. And if we sigh up to the US reg sphere we close the door on Europe ... Not so simple.
I personally think the EU doesn't care much about losing trade with the UK if it means it also needs to violate its four freedoms. The EU's trade with the UK is some 8% vs 50% for the UK with the EU. So they will suffer but can absorb it. Can we?
Reality is: the UK MUST pay. We have zero choice in the matter. we need the EU to cooperate on not just trade but aviation for example. Open Skies is an agreement between the EU and the US. If we are out of the EU, we are no longer part of Open Skies. Planes to and from the US and EU stop. Overnight.
Same thing with Euratom. Nukes are 26% of our power. Where do we get our fuel? Note that while Euratom is not the EU, it is administered by the European Commission ...
So we are gonna pay. Bigly. The downsides would dwarf the payment. £60 billion is nothing vs the alternative.