Sometimes fanfiction disappears because the author lost interest or faced legal issues. It can also happen if the hosting platform shuts down or removes the content.
It's hard to say for sure. It could be that the app didn't generate enough revenue and was shut down. Or maybe there were security concerns that led to its disappearance.
The possibilities are endless. Fanfiction can introduce new plotlines, reveal hidden backstories, or even rewrite entire events. It all depends on the imagination of the author.
Well, it varies a lot. Sometimes Prim could have survived or had a more prominent role. Other times, new challenges and relationships could be introduced for her. It all depends on the specific fanfiction you're reading.