Can't help you with the technical or medical side of this rattyratgirl but can tell you my best friend's husband has it. He is 53 and ran a half-marathon in the October and then 6 months later was in hospital fighting for his life. He has made a good "recovery" from that but has had to retire due to his health and takes many, many tablets per day (around 40) I think. He has to have a sleep apnoae (sorry, can't spell that!) machine at night and whilst his day-to-day living has changed considerably he is doing ok.
The hardest part for both him and my best friend is acceptance of his condition and that he is simply no longer able to do what he could before - but I guess that is true of anything that comes along and changes your life.
It hasn't been easy and he is such a poorly man but he copes and I wish your MIL all the best.