Storytelling wise, when you want to show the large scale effect of an action, you show the effect on a representative of the affected parties. >only see the effect of timeline change on a single individual from the future>she is wiped out
If the implication was that she was a unique case, then the alternative effects would be shown on other characters rather than leaving it up to the imagination of the viewer.
It works both ways too. Had Ashi not disappeared and also made a comment like "I remember everything as it happened, but I also suddenly remember a different childhood"(or something along those lines), then the implication is that everyone else is living a parallel existence in a better future.
Unfortunately, as it stands, the episode only provides(admittedly minor but still significant) evidence for the case of everyone in that timeline being wiped out, and zero evidence to the contrary. This really ends up leaving only one reasonable inference toward their fates.