Oh I didnt want to spoil anything but the first scenes are litterally him being “revived”. So he mustve died in de past. Its nothing bad or traumatic and you really should start reading!
The entire story is basically being told in 2 different times. Wei wuxians life and then again when he has been revived. Its great!
"Wei Wuxian successfully destroyed half of the Stygian Tiger Seal before his death. Jiang Cheng led the First Siege of the Burial Mounds[40] that resulted in the slaughter of the Qishan Wen Sect remnants[41] and Wei Wuxian's death from spiritual backlash"
So yeah. People speculate that the backlash would have disintegrate his bodies or that the zombies tore him to pieces. But we don't really know like you said just some clan leaders saying he died a horrifying death befitting of his crimes
Does anyone know if the novel actually has the scene of wei wuxian's death? I wanna read it. I feel like because he came back Im not fully grasping the fact he's been dead for over 10 years and lang wangji has actually lost him for a decade. the heartache omgosh