The EU is not being asked to accept any trade deal at all (hence no deal). A no-deal outcome is actually just fine, under the standard rules, the cost of food and other commodities is likely to decrease for consumers, and the EU is not going to blockade the UK. The UK hosts a considerable number of financial institutions which are crucial to the EU, so if they know what's good for them, they won't mess around with that too much either.

Altogether it seems that the downsides are acceptable, and the upsides are the same as they were when it was called to a vote. I don't really see what the problem is. The UK is going to do just fine, and so are the EU member states (whether they're in or out). I don't get why people have to make it out to be a catastrophe.