3 resurrected dragons(Vuljotnaak, Nahagliiv, Viinturuth) that have been killed don't disappear at all, no matter how long have passed, they are just invisible, but still can be interacted. However, these dragons do disappear in vanilla game without mod. For example, I can teleport myself to Vuljotnaak by using command "player.moveto 000FDBB1" for checking this bug.