Subsidies from the EU were never a major component in our national income, not to mention that reciprocation was in place by way of the CFP. I have great difficulty seeing the north as a standalone state in any capacity.
It would not be stand alone it would have EU backing and london and dublin help too. They could start down that road. Why not? No reason industry cannot exist up there just as well as here if they take a long term shot at it.