As for the Sabitsuki Ending, what happens on the roof is up to interpretation. I know a popular theory is it's one of those 'you know what to expect' implications and she commits suicide like Madotsuki, complete with the similar blood smear to clue the player in further. As for the Rust 2 ending, nothing is left to interpretation except where the Gas Mask Maid takes Sabitsuki. The Rust Ending 1 is thought to be simply a preview of Rust Ending 2, but is it? Personally, I think that Rust 2 is only achieved after Sabitsuki kills off the last bit of her humanity (she brutalizes a clone of herself, even!) and takes on the full Rust identity. The Rust 1 ending, however, is when her disease has become advanced but hasn't taken over her mind. Instead of severing her legs and all that, the Gas Mask Maid simply takes her to the hospital and she is passed out in the credits screen. Gas Mask Maids seem benevolent in comparison to the sesspool that is Sabitsuki's dream world. Something enjoyable like snacks and beverages is a big contrast from the grim that makes up most of the world. The Gas Mask Maid only takes her out in the Rust Ending 2 because she's violent and too far gone to cooperate with being helped. Just look at the Gas Mask Maids. They seem more like modern plague doctors than monsters. On the subject of Sabitsuki getting her legs cut off, by the way, I think that amputation is, for some strange reason, part of treating the disease and slowing its progression. There is enough severed limb and prosthetic replacement imagery in the game to back up the significance of amputation.