This is a difficult one.
You are getting €1,050 rent and paying around half of this in interest. So this is a very profitable investment for you. Each month, you are reducing the balance by €500. Each year, by €6,000.
If house prices increase, the increasing house price will meet your reduced mortgage balance at some stage, and you will be back in positive equity.
If you keep paying the rent in full, it's unlikely that Certus will repossess the house. They may want to, but in reality, they have worse cases to chase first.
I can't see why they would split your mortgage. This would effectively reduce the interest rate further from 1.95%, which is unreasonable to expect of them.
Extending the term will help, but we don't know how much, as you have not told us the term.
What country are you in? Do they have a bankruptcy regime?
You could consider asking BoS to allow you to sell your home and to write off the shortfall. They might go for it as you have moved abroad and it would be difficult for them to pursue you for the shortfall.
However, as you have a long term cheap tracker, getting a house worth €250,000 for €550 interest per month is very good value. It would cost you a lot more than this to rent it.
Stay in constant engagement with them. Follow up with a letter reminding them that they have not replied. If you make or receive phone calls, make a note of the date, time and the name of the person to whom you speak.
In the unlikely event that they do go for repossession, you will have a good file to show the judge and he will be slow to give them possession of your home.
If you get back to Ireland and you can start paying your mortgage again in full, they are unlikely to seek/get repossession even if there are significant arrears.
Brendan