@hhardy01
I don't see any feasible way to square the circle about Northern Ireland in the short term [0].
But with regard to commerce in general, is it really so dire? In the absence of a deal, won't the UK just continue to buy things from the EU? It's entirely up to the UK to impose import tariffs or restrictions, and the EU has no export tariffs, right?
[0] Long-term, it might be possible to negotiate a UK-EU free trade agreement, but that could take a decade.