If he had made a poor company investment and destroyed the amount of money at this time in your relationship you would not feel any directly to that cash now. He regrets it therefore is not likely to get it done once again.
I believe it is simply a additional thing (but a huge one) to fuel a dislike for MIL. Everything you absolutely need to complete is simply accept it just happened, be courteous and civil him but keep a guard up too with her for.
I don’t see what good may come of bringing it or what you will wish to take place being a outcome.