I went through the experience of the UK dropping out of ERM and having salary in GBP and costs in DEM so I know personally how painful exchange rate fluctuations can be.
I think that you are right to think that it could be scary, but who really knows?
Take heart in the fact that you currently have a Euro-valued mortgage, Euro-valued property, and Euro income, so you currently have no exchange rate risks. [Unlike some who already have a Euro-valued income, HUF valued property, and a CHF valued mortgage]
Unfortunately I don't think there's any financial instrument you can buy, simply because the Punt II does not exist. Any other instrument is also a gamble on exchange rates, which may make things worse rather than better.
But even if Ireland were to try to voluntarily leave the Euro [unthinkable] there's no defined mechanism to do so. Ireland cannot be "ejected" from the Euro either. It's simply impossible.
So we can only presume what could/would happen. My presumption is that even in the worst case if Ireland ever left the Euro [and I don't know how that would happen] then you'd still have a Euro-valued mortgage debt and a Euro-valued property, but possibly a Punt II-valued income.
At that point you could still presumably sell your Euro-valued property to pay off the Euro-valued mortgage debt, or not?
So is the problem really as big as you imagine?