I have read parts of this thread (I couldn't read it all as it is just too much to take in) and, like everyone, I am horrified by what has happened.
Being a compulsive gambler is an illness and certainly Neil is ill. However, whilst having sympathy for him because of that does not mean that he should not accept the consequences for his actions. I'm not sure whether there is any legal action that can be taken as, from what I understand, all the investors had an informal agreement and there is no law covering this. I sincerely hope that no-one takes any physical retribution as this will get you nowhere.
This may seem naive, but a possible way of retrieving some of the money is for the investors to stake Neil in one of the GUKPT main event games and, if he cashes, take back the winnings. At the end of the day he is still a good poker player and if you one of you was there to take the winning cash from him at the cash desk, you would get some money back and he couldn't go and gamble it on something else. As I say, perhaps it is naive, but it is a possible way to get some money back.