The damage over time never goes off and does not rely on Killteam to refresh the duration with attacks. Had Banshee rage trait on and Wraithknight quickstrike deflect. I'll post the replay if necessary.
Indeed, you're right. Just wanted to report that myself.
Those Banshees ran away, and de-buff was properly lifted on Scorpions which stayed - should be something about tic-times of Vortex and KT regular attack crossed. Maybe Flamer.
But this is a bug anyway.