i don't think that i'd be able to miss anything if i ctb, but i'll answer in terms of what i'd be sad beforehand about having to sacrifice.
kind of a shitty answer but honestly, everything. the bad and the good, the little and the large. feeling, experiencing, seeing. flowers, walking, animals, tea, eating good food, discovering new things, waking up - really all of the little things that feel insignificant but aren't when there's no way of having them any more.
i see my life as a gift that i'm unable to cherish for whatever reason, maybe i was the wrong recipient. it is unfair that i'd have to sacrifice everything that others experience simply because i'm incompatible with living and they aren't.