The announcement at the end seemed random to me at first, but upon rereading it, I notice that we already saw her fall and then lie on the ground bleeding, surrounded by scattered leaves. As someone in the other thread pointed out, a cat lands on all four; a human doesn't. It makes sense she'd realise in this moment the sobering truth.
The dead cicada, being a creature that normally "sings", I view as a sign her talent was already fading at the time, or an omen for what was to come (a slow decay).
As for Qiangyi, I suspect, since she wanted to break up some time prior to the admittal, that she's already been ready to move on for a while. I view the move-in scene at the end as her moving out from the old apartment to her own place, leaving behind her past fully. Though I can't help but feel that with her new girlfriend's style being very punk-ish, that she might be a similar type (some sort of artist).
Either way, really good story, love a good psychological deep-dive. And the metaphor the narrative is presented through I think is very apt. There's certainly an appeal in this kind of self-destructive behaviour, which often rewards unwarranted attention and affection, and I suppose I relate somewhat. Feeling like you can't take care of yourself, like your life is falling apart and the only solace you have is getting into a drunken stupor and hope your S/O is willing to pick up the pieces.