I accidentally deleted my Epic Quest. Fortunately, I am/was still in the Prologue. Can I get the quest back without starting the entire line over again?
You should be able to go back to the person who gave you the quest you deleted and pick it up again. Any progress on that particular quest is lost.
You can use this wikipage to find out who gave you the quest you deleted. If you are unsure which was the last quest you completed in the prologue then you can open your quest log and tick the "Show completed quests" tickbox and find the Prologue category.