I have a very good friend who lost her sister to a rare cancer at a very young age and had it loom over their families head for about a year. They celebrated her life the whole year as much as they could. And were around her every minute they could be but never stopped living their own lives which is what she wanted and told them this.
It was not easy when she did pass. But everyone got to say thier good bye's and that is something we don't always get to do, so in some way that seems cool that you will get to do that. No regrets you know.
My prayer's are with you and your family as well. I hope it is an easy transition for all of you.