The biggest losses for the EU are likely to be on the front of security co-operation and Europol, Britain is one of the largest if not the largest contributor to it with something like 40% of its cases having some British involvement, no deal on that results in our information being permanently removed from its databases. UK intelligence services have generally been more effective than say those of France or Belgium in preventing truly devastating terror attacks, obviously no security is perfect and bad things still happen
You are correct in saying that the loss of the British Economy wouldn't hurt the EU fiscally as much as it would hurt the UK, the loss politically would be far worse, with squabbles over money, projects being cancelled etc taking centre stage. Then there is the direct job losses for industries which rely on access to the British market and territory for example fisheries, on a spreadsheet the numbers look small, when you remember it actually involves real people with votes (not that i think the EU gives a shit about about democracy, that's always been just an irritating inconvenience to those who run it) but the people elected to run its member states sure as hell do. The financial services sector derives about 20% of its revenue from the EU last time i checked so that's actually not such a big deal when compared with manufacturing and supply chains. You end up with faintly ridiculous things like airbuses not having wings as they're manufactured in the UK.
Ultimately if negotiations break down no one wins and no one can actually predict what the final outcome will be but it certainly wont be pretty and no one involved gets to walk away with their reputation in tact and the world will be a more dangerous and unstable place as a result.
About the only thing that anyone can say for sure is the events of last week have only strengthened the resolve of those who voted to leave and meant it, so thanks whoever leaked the bullshit about last Friday's dinner you've just handed the conservatives a substantial majority in the upcoming election.
I hope your buratino's die screaming.