If you move to Donegal and are still working in Northern Ireland you will continue to be entitled to the same routine NHS treatment. When you retire this would generally not be the case. As a cross-border worker or "frontier worker" resident in Donegal you would also be entitled to an Irish medical card from the Health Service Executive in the Republic. This would entitle you to free public healthcare in Donegal and you should be able to retain the card when you retire on the basis of having a UK Retirement Pension. Although automatic entitlement to an Irish medical card kicks in at age 70.