personally, i've not come up with my own answer. at first, i thought it would be easier to know in advance, but then EVERY time i was with that person i'd likely be thinking "oh my gosh, i only have _____ left with them. i can't lose them. i don't know what i will do without them"
on the flip-side, while my mom was in pain and in a bit of a weakened state her last week or so of life, i had gotten past my fear of her death (with encouragement from doctors) and enjoyed, laughed, loved, joked with my mom even the day she died... if i'd have known she was going to die that weekend, i'd have been crying and upset the whole time and wasted my last hours with her....
this is probably one of those lose-lose situations (actually, i know it is because you lose somone)... but it doesn't have a 'right' answer.
that's why i just wondered how everyone else felt.