When my father was terminal, I stayed with them to help, and then to keep my mother company after he went into the hospital for the last time.
I figured, if the doctors can't do anything else, I sure can't; I decided that my mother was now my patient.
You're your mother's child as well as your father's. You've done your duty by your father, and now it's your mother that needs you.
As for "wanting him to die", he will do that whether you want him to or not. We all will. What we can want, is an orderly transition into the next phase, whatever you believe that is.
Be by your father's bedside as he moves on, and then by all means load your mom onto a cruise ship, take her someplace relaxing, let her meet other widow ladies she can bond with.