I think Vriska didn't die because (I think this is cannon???) The higher on the hemospectrum a troll is, the more beatings and stabbings they can take before dying. I mean, it could be true that all trolls are hardier than humans but I thought it was a hemospectrum thing. Like lowbloods aren't as strong and can't bleed out as much but they have cool powers, highbloods are way stronger and have sharper teeth and horns. This might just be a theory I've made up but I swear it had some sort of canon

It’s common fanon conception that Higher Blooder Trolls are generally stronger and tougher, but this is also heavily influenced by the fact Gamzee exists, so take that as you will.