As an act of revenge, EU might ‘help’ Ireland. But that means a large initial investment, which EU doesn’t have, or won’t have… Besides, a see-saw battle is not going to help EU either, as itself is also struggling at the moment.
I have been to Dublin, which is lovely itself. Don’t know very much outside Dublin, but as far as I know, not so good. A lot of factors will be involved if companies were to move to Ireland. For example,
First, the infrastructure needs HUGE improvements. Where is the money from? And how long does it take? Even the physical infrastructure is ready soon, is the human capital able to cope?
Second, companies need to justify their reallocation costs, which is BEYOND HUGE. In a lot of cases, the destination needs to provide some sorts of ‘compensations’. Can Ireland do that?
Third, do people want to move? Would you want to move to Ireland knowing the infrastructure is not up to scratch, that your kids might not have a good school to go to, and etc? Bear in mind, the moving involves lot of families, not only one that you can simply enroll in a good local private school. Living in Dublin is quite expensive, too. Oh, as some mentioned, the weather is not better either.
Besides, IF the UK government performs, a fair negotiation with EU and policies like lower Corporation Tax (of course, not only this) should give London a larger chance to keep those big companies. Even not, I think other big European cities still have more chances than Dublin.