(I don't know any player on earth who would not immediately kick the ninja's ---es and then got to the village and kick all those ninja's ---es too.)
I do. God help me, I had a player once who just drove a campaign into the ground in situations like this, purposely steamrolling away from ANY plot hook. He was in a situation kind of like this where some guards they KNEW were corrupt and working for an evil sheriff showed up to shake down the party. This guy laid down all his weapons and walked away.
After enough of his shenannigans I just handed him the game. He had more fun running and setting his own plot hooks; I had more fun not fighting him.
That's just shy of punching the DM in the face when he asks you to roll initiative.
If the rest of the players were happy with the job you were doing, I'd have talked to them, and to the guy privately.
Maybe say to your other players, "Guys, I'm trying my best here... but Josh seems to hate all my plot hooks and actively rebels against them. Am I doing something wrong?"
When they say "You're doing a great job."
You say, "Is there anything you guys can do to help?"
Eventually, when push comes to shove, and he does a thing like tosses his weapons down and walks away, just say, "Josh walks down the road and out of the fight... everyone stares in disbelief for the next 10 minutes until he's a pinprick on the horizon, a mile out of the way."
Then have the fight. Make it a nice, long, tactical fight and just keep skipping the guy when it's his turn.