Having just had Azjol-Nerub come up for the first random today I was expecting pretty simple, but boring run.
Having been pretty uneventful upto the trash prior to Hadronox we just seemed to be proceeding like normal, when suddenly he prior to us pulling him, or so I thought his health was dropping very quickly and was killed by the spawns, at which point he just despawned.
This was blamed on the hunter pet since apparantly the pet took the brunt of the aoe leech poison which normally heals him through those adds.
First time I have seen that happen, and while it was 1 less emblem it was for entertainment value worth it.