The situation is unfortunately unclear.
If the withdrawal agreement is adopted or the Brexit deadline is extended
If the UK's EU withdrawal agreement gets adopted, then 29 March onwards is a transition period and things are basically unchanged from now and there's nothing more to say. But given the current political situation (in particular, that the UK parliament recently rejected said agreement), assume this won't happen unless proven otherwise. Similarly, if the Brexit deadline were to be extended then the UK is still in the EU for a while and things are again unchanged from now, but we don't know if that will happen.
No Deal Brexit
There is a significant risk of planes not flying after March 29 date due to Brexit tearing apart the UK's aviation regulation regime. I don't know whether to say to expect that or not, things may be clearer nearer the date? If you do travel, make sure you have a plan if you're stuck in Ireland.
Right to re-enter the UK
The settled status scheme for EU nationals is part of the law now, and the test phase of the scheme is open. If you have an EU passport (not ID card, they didn't make the scheme work for those yet) and are willing to pay the fee, you can apply right now. If your application is a simple one and succeeds before that date, then it's very unlikely there'd be anything to worry about insofar as re-entering the UK.
If you don't have it by that date, well, until the law is changed, you still have the right to enter and be in the UK as an EEA national. That change will be carried out a bill currently making its way through parliament, but it's unclear when, because the repeal of the EEA rules by that bill comes into effect at whatever date the government later chooses. However, the government has said it will give EU nationals until the end of 2020 to apply for settled status, so I would expect you won't need special documentation to re-enter in the meantime, but alas I don't know for certain.
Do make sure you have more than 6 months remaining on your passport. They may be more picky after Brexit.