A couple of comments.
1) The PPR counts as a Family Home. In your friend's case, "a family of one".
2) There may not be a need for a PIA. First thing to try would be for your friend's PIP to ask BOI if they would accept €10k in "Full and Final Settlement" of the €100k shortfall. BOI's public statements indicate that they won't, but in practice, behind the scenes, they might. This would be known as an "informal arrangement" in that it doesn't make use of a legal process.
3) A "no-veto" PIA would work but your friend must have been in arrears on his PPR on 1 January 2015. Failing that, a DSA might be a runner as all debts appear to be unsecured.
4) Plus one to Brendan's view that bankruptcy is not needed here. It's important that your friend does not go bankrupt as the sole owner of a PPR has a higher risk of losing their home in a bankruptcy situation than a couple who jointly own a property and one goes bankrupt.
5) Putting forward a PIA/DSA is a valuable exercise. Even if it doesn't get approved the fact that it was proposed can be used to successfully defend subsequent bankruptcy proceedings brought by a creditor. This is because creditors will usually receive more under a PIA/DSA than they would if a bankruptcy order is made.
6) Keep encouraging your friend to keep the chin up. It's all there to play for. If he wants to keep his house he will.