Many people with high mortgages can only go down the route of repossession unfortunatly.
To sell the property below the outstanding mortgage value will require the vendor to hand over thousands of euro’s at the Notary to settle the mortgage. If they had that kind of money they would be able to continue paying their repayments.
If they allow repossession at least they can skip off without having to find a shortfall.
Many people are doing just this at present. Who knows if the banks will chase them for the outstanding balance, most will go to ground and be difficult to track and the banks are so inundated with defaulters that it could take years to find them.