It's a tough problem with a VTT, because so much time has often already been spent making the go right choice optimal fun. Maps and monsters are laid out, and so forth. As a player who spends a good portion of time also being a GM, I realize this and do my best to pick up on clues dropped by the GM to follow the optimal path. It's part of the social compact we follow to make the game work at all. Otherwise, we'd all be in the town running taverns and bakeries. In this particular case, if you are the designer of the adventure, try to design for choice. Don't eliminate it; that would remove player agency. Have content both left and right. Ideally, either way could further the adventure, but in a perfect world, they would need to go both ways, and the choice becomes not "which way do we go?", but "which way do we go first? " If you are comfortable with the approach, there is a method that can work very well with Roll20. Instead of mapping out an entire dungeon, map out individual rooms or short room complexes. The corridors in between are theater of the mind. That way, you can arrange the order they are encountered on the fly. Was the last encounter a brutal meat grinder? The next room they encounter is empty and defensible, suitable for a rest. Do they need a clue as to how to proceed That abandoned study with the bad guy's orders to his lieutenant left carelessly on his desk is next. It's also suitable for mega dungeons. Frodo and Co. would never have made it through Moria if it were laid out like Undermountain. Instead, the adventure is laid out in set pieces: The Watcher fight at the West Gate, The few rooms around the Durin's Tomb, The bridge of the Balrog, and so forth. Everything in between is narration. I did this recently with a "lost city of the drow that became an abode of monsters" adventure and it worked quite well on Roll20. It also allowed me to keep all the maps of manageable size and to reinforce the feeling of being lost underground.
