If you happen to find yourself stuck, you'll have the option of using gems to restart the maze. While this will both clear your parties and restore your defeated heroes to health, you'll have to restart the maze from the very beginning of the first section of the first level. You also won't be able to recollect rewards for sections you already completed and received rewards for before restarting. However, assuming you get further after restarting, you can collect rewards for completing new sections.
Restarting won't affect the maze version or its elements and monsters. The Dark Maze changes only when it reshuffles every three weeks.