First of all, he has absolutely no need to worry about losing his house. He won't. The only thing he has to worry about is his credit rating.
He has to contact Bank of Ireland as soon as possible and notify them that he has a short-term problem.
In the past, a phone call would have sorted this out and they would probably have agreed a 3 month full payment moratorium over the phone. Now, he will probably be asked to complete a Standard Financial Statement to apply for a moratorium. The banks are all snowed under, so he might not get a proper response before he goes out ill. He should try to resolve it by phone first, but it will be difficult.
If he gets their agreement to stop or reduce the payments, then his credit rating won't be affected.
He should follow up any phone call with a letter saying that he won't be able to pay and that he is stopping his direct debit until his income recovers.
Depending on his circumstances, they might extend the term of the mortgage to reduce the payments.
He will get a more meaningful answer if he fill out the following
Standard Format for unsustainable mortgage Case Studies
Brendan