In the beginning, to get a warlock quest you would go to the warlocks cave and roll a die there on the chart printed on the space. If you didn't like the quest, you could use fate to reroll. Obviously you can't roll a die the get a quest from a deck now that they've added the new quests and quest rewards, so does that mean you are now stuck with the card drew, or can you use a fate to draw another card and keep it

I think that may be the official rule - but we've always played it that if you make a return visit to the Warlock's Cave, you can exchange your Quest for a new one.

Yes, there's a variant for replacing Quests. I believe if you visit the Warlock's Cave again, you can replace it.

Although replacing Quests can make the game much easier, as you can shuffle through the deck until you get the Quest you want.

We only replace a Quest if it's impossible to complete. Let's say, "Take 1 Life from a Character" in a 2-player game, where the other player already hit the Inner Region.