Maybe because he isn't the vengeful and demented person that is his sister!
What do you mean "he has nothing to lose?" He may shortly be meeting his Maker. Would you want to go to judgment with such a sin on your soul? You know there really will be a reckoning some day when we all stand before the Judge of Heaven and Earth and account for our actions.
So you're subtly suggesting he should kill her?
Me, I'd just await my fate and make my peace. The sister will receive hers in the end.
Payback. I'd start by working through her kids. I'd be calling them and sending them mail saying stuff like, "you know your mommy's gonna let me die? Your uncle will die because your mommy won't help him."
I'm serious. If she changed her mind, great. If not, I'd at least have messed up her relationship with her kids.
I don't think that's any colder than what this woman is doing.
Maybe he has something she doesn't? A conscience?