After defeating Sadal, you should get a quest called "A Letter for Deshaan", which takes you into the next questing zone (Deshaan). Deshaan is a Level 16-23 zone, so you may want to finish off any side quests in Stonefalls before you go. (You can come back at any point later on as well, but enemies will no longer drop loot or XP when they are 5 or more levels below you.)