Boris could withhold the 39 Billion. The EU would likely take the UK to court but that's a case that could take years to resolve and who knows who would have authority to rule on it. The UK could in the long run end up having to pay more, its all very messy. Not to mention the damage not paying its financial obligations would do to the UK's reputation. Yes the UK has a trade surplus but so does Ireland have a trade surplus with the UK but we are not silly enough to claim that leaves up holding the cards because we are a much smaller economy than the UK as is the UK to the EU, so the % loss of trade will be far greater on the UK side than EU side. Its basis maths at this point.
The Secretary general of the international chamber of commerce Chris Southworth has said he can not see the UK getting back to reaching the number of trade deals they currently have via the EU for at least 20 years. Even a trade deal with the US would not offset the loss of trade from having no deal with the EU.
Have you see the forecasts for the UK economy in the event of no deal from rating agency Moody's, the IMF, the UK treasury and the office of budgetary responsibility (which was specifically set up to remove political influence over economic forecasts). They are not pretty, anything from a loss of £30 to £90 billion loss to UK economy, recession for 1-2 years GPD growth drop of between 3-9%. Have you seen the comments from the current and former head of the WTO who have said the UK moving from trading via the EU to WTO terms would be hugely problematic.
But I doubt any of what I say matter to you or to no deal Brexiteer supporters.
I'll ask you the following question. What would you consider a successful outcome or a no deal brexit be and what would be a failure.
I would say a no deal could be considered a success, if there was only a minor dip to the UK economy and it recovered say within a few months to a year (economic growth returned). That jobs losses where only in the low thousands. That delays at ports and borders be resolved in a few weeks to say about 3 months. That there is no significant issues with the NI border. That a trade deal with America and other major economic power was signed within say 2 years. Even if economic growth in the UK isn't as good as the projections for the UK remaining in the EU, but are say almost as good or even half as good, I would say well that isn't too bad maybe it was mostly project fear.
I believe they would be pretty quick indicators on whether the warnings where exaggerated or accurate.
But for those advocating for a no deal. Will you stand up and say we got it wrong if the the warnings and forecasts are accurate.
Brexiteers have gone from "a trade deal will be the easiest in history" to "we have nothing to fear from no deal" and now are moving to "its the EU's fault if there is no deal".
Also Boris is more of an Ivanka Trump!