For me, I think one of the saddest moments of the '90s anime was when Queen Serenity died and had the Moon Kingdom inhabitants reincarnated on Earth. Zoycite's death was also heartbreaking. I haven't seen all of Crystal yet, so I can't really speak on that.
I'm assuming she intended for Sailor Pluto, Sailor Saturn, Sailor Uranus and Sailor Neptune to replace Sailor Venus, Sailor Mercury, Sailor Mars and Sailor Jupiter. Maybe? Possibly? That would've been interesting.