It sounds to me like you are either upset that you are not winning, or that game night “ends too early”. It also sounds like this may not be the game for your group. I say this because it clearly does not have the ability to give your group the experience you want without some very significant modification.
You also seem to be skipping over one of my major points. If Janet is inflicted with Pyromania SHE DOES NOT HAVE TO START FIRES. It is a choice. She can continue the investigation aiding the team in her (hopefully) usual way. She technically will not “win” if the investigators succeed, but then again, she should not. She went insane. She should be punished for doing so. As should everyone (in the game that is, in the real world they should be rewarded!). Managing sanity should be a top priority. Yes sometimes the game just doles out sanity for no reason, but that has to be taken into account.
And finally, if the game abruptly ends because one of the players is inflicted with Pyromania (or any other condition) your group has not been paying attention. The whole group knows when a player goes insane. They may not know the infliction, but they know it has happened. The rest of the group should be keeping an eye on that person, making sure they are not up to no good. There are things you can do if you think someone is working against the team.
Edited by LabanShrewsbury