I'm thinking of enabling my sister's mistreatment of our elderly abusive father until his death
Why would you help your sister to mistreat your elderly father?
Because he's abusive, and I think the less time we have to deal with him, the better.
If your sister is abusing your father, you should talk to her and try to intervene, not help her to abuse him. If you both are too close to the situation to care properly from your father because of your feelings, you should let others care for him for the benefit of all of you. It is unhealthy for any of you to be in an abusive situation.
I just want him out of my life so it isn't my problem.
It could be your problem because you and your sister could be arrested. You need to make sure that this doesn't happen.