I feel for ROI, none of this is of their making. They are the only country that will have a land border with a potential non EU country. No wonder they are miffed.
Ireland itself could possibly do very well out of Brexit.
Many city banks, insurance companies and other organisations have already made deals to move from the UK to Ireland. Many more will follow suit.
uk.businessinsider.com/12-city-banks-relocating-to-dublin-after-brexit-2017-6
The same will apply to other sectors of the economy. Research and high tech would be particularly vulnerable here.
Ireland has also gone after the European Medicines Agency. If the EMA leave the UK and move to Ireland, many Pharma companies in the UK will do likewise:
I'm not sure if it will pull this one off, but if it does, it would be a major boon.
Northern Ireland, on the other hand, will be in a very precarious position. Its economy could be decimated.