Firstly, I'm sorry for what you've lost. Losing a family member is never easy. However, though it would definitely have been better had they not died, it was probably for the best that it was an illness and not a person, because if it was a person, I'm sure that no amount of revenge would be enough. You could destroy their life entirely and still feel empty. As well, with a person, you would probably be questioning yourself on what you could've done differently to save them, whereas with something like illness, there's likely less questioning involved. I'd much prefer to lose someone of natural causes then through human action, but that's just me. Of course, I would prefer to not lose them at all, but unfortunately loss is a part of life.