Do I have any recourse if a will has not been followed?

Each state is different. I am a California attorney so my answer not be suited to your state. Generally speaking her last wishes should be in writing. If in a valid written document (a "will" for example) they should be followed. If there is a written document and her wishes were not followed then the question is what damages you have. Are there assets you should have received but step dad kept them? Or is it more emotional damage (hard to establish) that he hid your mom's illness and didn't follow her wishes? In any event I would talk to an experienced probate attorney in the area where your mom resided. Good luck!