`Any player who does not control a hero with at least 1 clue objective attached cannot commit characters to this quest. If there are ever no heroes with Clue objectives attached in play, reset the quest deck to stage 2B.`
The wording is a little foggy here.
Does this mean if you have three heroes they all have to have at least 1 clue, or, you cannot commit any characters to the quest?
It says "player" so only 1 of that player's heroes need to have the clue to be able to commit any of this characters to the quest.
If only 1 player (in a multiplayer game) has a hero with a clue, only that player can commit his heroes to the quest. The other players will have to just attack and/or defend or do other things besides commit.
If none of the players have a hero with a clue, then you reset the quest deck.