It maybe knowing the answer will eventually help your daughter although it can take a while and Christmas, children's performances, school nativities are such a tug to the heart. 
In my early 40's I had surgery, it was thought surgical stockings were not needed. The blood clot to my lung was only picked up a couple of days later, I had no symptoms, luckily it was found during an investigative scan. I had to be told about it as I needed warfarin for a number of months afterwards but it was without much acknowledgement of responsibility from the hospital. I took it no further but I'm so very sorry your son in law passed away. 