And makes it easier to implement negative interest rates for depositors.

cashless banking means that one is getting a haircut on their savings, and the only thing holding back negative interest rates is the physical cash in circulation.

if anything, I see more ATMs popping up all around the place in shops/bars , the use of outdated and unsupported operating systems mustn't be a problem then.

Maybe in a corner shop run by the owner. Won't happen in a Tesco or Spar. Till is linked to stock control; double they'll even keep the door open without power due to liability, no CCTV, etc.

I spend a bit of time thinking about this stuff because I'm secretly a bit of a prepper. IMHO losing power is the worst utility loss we could have. In addition to the stuff you pointed out above, most modern gas boilers won't light without electricity, not to mention thermostats and immersions not working. A large number of people in Ireland would struggle to cook food or heat their house or water without electricity. Within 24 hours you'd have lots of cold, hungry and pies off people.

After two to three days of wide scale power outage you'd start to lose telecoms of various sorts, starting with mobile but ultimately some datacenter-based stuff too if it went on longer. It would not be pretty.

Things like water, gas, or petrol would be easier to deal with in terms of a week's outage IMHO.

Oh, I'm fully on board here.
Let's not forget all the fancy Dan new water pumps that won't work without electricity.
During Ophelia, we had no options for heat (gas), electrical generation, cooking (electric hobs) or water in the modern house I rent. No mobile or wireless. Can become vulnerable very quick if not into prepping.

People don't prepare enough for low-probability, high-impact events.

The decision to nix the proposed LNG terminal at Foynes a few years ago was a huge mistake.

How likely is an extended Island-wide electrical blackout? When we were putting in our kitchen my da told us to have an electric oven and a gas cooker that way you'll always have something to heat water/cook on.

You can get camping gas stoves easy for a €10 from halfords and enough gas for a few days of cooking and tea for €10.

Going further OT - but "local storage" is already required in the current infrastructure: pretty much every house has some water storage / buffer tank in the attic. Something I haven't seen in any other (continental) European country. So apparently we accept that the water infrastructure is crap and very likely to fail, otherwise why do this?
You could argue that it is therefore only a small step to put in a local gas and electricity buffer. Arguably the engineering is more complicated.

If you have oil you already have backup heating. I'd imagine there are safety concerns around storing gas and electricity onsite.

Most oil burners are controlled electrically. I know mine won't work when the power is off.