Quests that you cannot drop will never go away. You must complete it to be able to move forward in the higher Era Quest main line.
However when you move up Era, you will get the new (defeatable) quests series and will get to the recurring Quests of your current age.
(if you have done any of that Era Continental Map.
The Quests are tied to the Continental map)
Quests are a bit strange in the way the behave.but if you cannot cancel one, you must do it to move forward. but there is no penalty for never doing it. All that happens is you get stuck at that point (but only in the main Quest line)