What happens if bloodflow is completely cut off from the inferior vena cava?

I know it cuts off circulation in the legs and whatnot. how would a person die? Would their heart stop? I'm asking because I have a family member who has less than a month to live and she has a renal tumor that's pressing on her inferior vena cava, causing edema and rapid heart beat. I want to know whether there will be suffering or if her heart will just stop when it comes to that. Please let me know so I can have peace of mind.