Been down the malpractice road before.
Father had joined the class action, thus removing his rights to go after them on his own. Such suits are for the whole and not the individual. They would already consider illness caused, long term problems, deaths of various individuals, and side effects that would or could eventually cause death.
He had signed on and is part of the whole, when the group settled your friends father also settled. Settlement agreements do have such agreements as no future suits from any of the parties, including deaths attributed to it etc.
This would most likely preclude your friends fathers children from going after the company for wrongful death.
Now onto the other portion. If your friends father's partner was a "life partner" etc. Been with him for many years, stuck with him through the sickness, and all that goes along with it. Basicly did everything as a "wife" would have done. He could easily argue that the money is indeed his. Specially if they shared bills, and other monitary issues. This of course if there was no will.
How the check was cashed could be an issue, unless they did have a joint account, yet if they did again see above.
The only real recourse I see is going after the partner in civil and probate court. With a very big but. If the kids were not at his side, ignored him or would not deal with him because of his chosen life style expect to make a few lawyers rich over sour grapes.
Just my
