Krark the Thumbless + Discover

If I control [[Krark the Thumbless]] and I cast a spell with Discover, such as [[Hit the Motherlode]]: if I win the coin flip and successfully copy and cast Hit the Motherlode, when the Discover triggers resolve and I choose to cast the discovered cards from exile, if I fail those coin flips will the cards stay exiled or will they go to my hand?