This is, in my opinion, the saddest death in Warriors because Bristlefrost isn't even in StarClan. Rootspring, Ivypool, Fernsong, and any other cats who loved her will never see her again. (Ivypool's Heart spoilers!) At least Ivypool found out that there is existence after StarClan, so she has the comfort of knowing Bristlefrost is at peace.
If you have any warriors related projects, feel free to advertise them in the comments!