I guarantee you that there is no bug with vitality and damage as it is right now. Heads, necks, and chest areas that are destroyed will always result in an instant death, even if you didn't lose all of your health points.
It must have been hell of a hit to kill you instantly if you had 70% health. Of course, you may be mis-perceiving the health range -- it may have been closer to 50% or less health you had remaining. Furthermore, you may have died from blood loss (succumbing to your wounds), not from the jungatha's attack itself. Blood loss is pretty severe when you're missing a (or have a completely destroyed) body area.
As far as dragging having a roundtime, I didn't realize it did. However, since Healers are going to be coming out very soon, if you guys would like to persue an NPC healer to move out to the islands for you, you should speak with the prince and petition your cause.