Ugh... complicated! In many ways a united Ireland would make a lot more sense, but the prospect of all that violence starting up again is pretty scary.
In some ways, but the people of NI have never come anywhere close to wanting a united Ireland. For two reasons: culture/identity and economics. The first has become less important as the proportion of the population that is Catholic increases. Not to say that British identity isn't still very important to many people in NI, just that they make up a lower percentage of the population than they used to.
It's been known for a number of years now that the key to maintaining the Union is Catholic economic unionists. People who don't necessarily have any emotional attachment to the UK, nor even identify as British, but who would prefer to remain because they think they'll be financially better off. Even the likes of Peter Robinson of the DUP identified this a while back. If a bigot like him understands that he needs to woo Catholics who hate him but like the NHS and their pensions, more moderate Unionists who don't think papists have tails obviously will get it too.
Of course, this only works as long as the UK is more financially attractive than ROI. We've never seriously seen that not be the case before. I'm going to risk being blamed for causing a recession by Brexiters on happy pills here, and say that we're entering a period of uncertainty where the economic case might be undermined. Or at least, people might think it will be. So those economic unionist votes are up for grabs. And not all economic unionists are Catholic. There are Protestants who don't prioritise a British identity above all things, and might consider reunification in the event that ROI looked like giving them a better quality of life than the UK did.