Okay, so it seems the world explodes(?), and then it's brought back, and all of the Senshi and Usagi's classmates are going on with their lives, not realizing anyone is missing. Then they all remember and run to a bridge, where Usagi meets them, and Mamoru and the cats are waiting on his bike.

So...what exactly happened? Did they get thrown back in time? Minako is alive and apparently just now recording "Cest La Vie", which was already available on the radio in Act 1.

Did everyone remember Usagi and everything that's occured? (Makoto and Motoki are together in Special Act.)

the ginzuishou restores everything to the point it was before all the mess. so now, minako can take her cirurgy earlier and not die. but their lives have already been touched by Usagi. and they have that feeling that something is missing. and being senshi, even without their superpowers, they feel Usagi, and end up remembering HER.

and then, Mamoru gets his life back, because Usagi would never live without him. plus the shitennou help him with that.

So...did nothing that happened during the series actually occur as far as the timeline is concerned?

it did, but only in their memories.

at least, that's my theory.

i mean, i can change my opinion after i re-watch it again, but

I personally believe that that the timeline changed, that is an alternative reality that was no longer pre-determined by fate began but a future that was up to the girls to decide for themselves.