Overhaul the dungeon as follows:

• The endgame is extremely dangerous, to the point where it will kill most heroes by default no matter how well-prepared they are.
• Every branch you complete removes an aspect of the endgame’s danger. (Not specified if the existing dungeon branches count towards this, or if they should only be new branches.)
• Branches are themselves dangerous, and each one requires a non-renewable resource to “unlock”. Not specified if this resource is the same or different for different branches.

The idea is to create different choices and tradeoffs, and to force the player to take uncomfortable or unanticipated routes.