All the EU can do if the UK tears up the WA & there is, thus, no trade deal, is to hold its nerve, stick to its principles, remember that the long run is what really matters, refuse to grant the UK the short run palliatives it will seek, & accept the consequent short run costs. https://twitter.com/RonanMcCrea/status/1303947754276892674
Those short run costs will be particularly high in Ireland & some will argue that the EU should therefore give in to HMG. But the long run costs of doing that also risk being particularly high in Ireland. People should hold their nerve & remember where the balance of forces lies.
All Europeans, especially those living in small countries, and especially those living in small countries beside troublesome neighbours, benefit if the EU acts collectively and makes it clear that there are certain behaviours it won't tolerate from the Johnsons, Putins & Erdogans
All small countries are safer in a world where international law is respected. And all European countries are either smallish, small, or very small. Respect for international law is a core EU value and this is an issue worth making a stand on. Even if it implies short run costs.