Loving the new update btw. But a few things rise now. First off all main quest boss or mini boss encounters can be spoiled for others if one progresses too far without contacting other players first and can even happen by accident if said player doesn´t know the storyline.
That said let´s dive into this topic a little more: why is it not possible to resurrect said bosses in their arenas, let´s say 1 per day? All it would take is a glowing symbol in their arena which you can interact with and restart the fight (cutscene included).
Another going in tandem with this is would be something like cutscene-player ingame for those who might have missed a part of the story for their busy real life.