To address some of the earlier questions....
The encounter with the crazed despot hadn't been going on for long (only a few minutes). There had been a string of roleplay heavy sessions leading up to it, however, with most of them having only a combat or two - so the boredom may have been setting in over a few weeks and this had been the tipping point. Still, I try to communicate to the players at the start of the campaign and check in after each session to make sure they're having fun.
The hot-headed player who seemed to get bored with the encounter also happens to be a good friend I've gamed with for more than 20 years. It's not out of character for him to do something irrational like this, but this isn't a dungeon hack without consequences, something I've tried to instill in the group. The other player (would-be assassin) just went along with it to try to salvage a bad situation in the heat of the moment.
I had put them in contact with revolutionaries in the town over the past couple sessions. The more extreme faction (who called for the removal of the ruler) had been blown off [strangely, by the hot-headed player] and the party had been unwilling to take sides.
A lieutenant of the mad ruler even offered to return the weapons to the party and free them from the stockades under the promise that they leave town and never return. He said he would just tell the ruler he had killed them during an escape attempt, because even the lieutenant was tired of all the bloodshed. [And I feel like this was giving in too much as a DM.] Even this compromise was unacceptable to the hot-headed player.