Board Thread:Questions and Answers/@comment-31067473-20170714200704/@comment-27136653-20170809020058

Flowey was created after at least two humans fell, since Alphys spoke about extracting the DT from souls (plural). Still, the most important fact is that Flowey never met any other human besides Frisk (if we exclude Chara of course). So then, Flowey MUST have been created after the 6 humans fell. This is further supported by the fact that the time between the 6th human and Frisk was apparently long enough for the monsters to become too desperate, which led the king to hire a new royal scientist (Alphys) to find a solution for the situation.

And also, ALL humans could save and load, since after we reset once, Toriel seems to slightly remember us, and then says that she has already experienced this with the other humans. Other characters also experience this deja vu when we reset. So if Toriel did experience this with the other humans, then they must have had the power to save and load also.

But why are they dead then? That can be answered the same way as the question why is Chara dead can be answered. They willingly gave up on their lives. But why? Well, perhaps Asgore was too tough for them. Back then he didn't want to kill any humans, but had to, since what else was there left to do? But after the 7th one, he is so fed up with it that even we can defeat him.