Inevitable?

This will sound heartless but.... despite my dad's carefulness and pickiness in eating and exercise, I just feel that he will go before my mom... even though my mom will eat almost anything. I would like both of them to go together at the same time so that one doesn't have to be sad without the other, but it seems more realistic for one of them to go first. And I feel it would be my dad for some reason. My mom has a more pure heart and a very strong will.
Also her motherly love drives her on.