Should we remove the disruption if all the Mafia members are working together to kill? Or should we remove the failed assassination attempt on an ally? In the first scenario, we would have between four and seven potential kills in one night (three Mafia, a Serial Killer, a Marksman, a Scientist with a Bomb, and a Vigilante). Fearing a massacre, I want to introduce the disruption. Combined with the possibility of blocking and a discount on caution, this could provide a perfectly optimal result, as in any normal Mafia game. Another factor is that there is only one non-killing role for three Mafia members, besides the kills themselves. Although, I'm not sure. In the second scenario, the alliance simply wouldn't make sense. But there is a concern that the ally might be revealed and then simply killed after the alliance expires.
It's an unconventional idea, but I'm afraid it will be difficult to balance.