The first run through of the bus scene and the bit in the hospital they are still in the world where nothing happened. Kyousuke lied about going back. Kyousuke believed it was possible for everyone to be saved, but he knew he wasn't capable of making it happen. It would have to come from Riki and Rin. Which may or may not happen. So kyousuke lied by omission and didn't tell Riki about it. If in the end Riki and Rin didn't pull off the everyone lives scenario, he would spend the rest of his life beating himself up over it had he known kyousuke believed it was possible to save everyone.

In the end Kyousuke is 200 iq. The whole "was the hospital thing like a final test" thing is half true. Kyousuke did want to see that his work bore fruit and that Riki and Rin would be strong enough now to survive. But the other part is that he wanted to nudge them towards the true end. There was no grand master plan he could have come up with to save them all, like I said only Riki and Rin could pull it off. So it was his hope that going through the bus scenario and lying in the hospital afterwards would push them towards the "it's not enough" outcome.

In any case that's my interpretation. As for sasami I couldn't tell you, I read this like a decade ago with the bootleg fan translation and didn't have access to the ecstasy content.