The rules of Mafia do not allow suicides. It is not permissible for someone to flip their card over unless duly convicted and asked to do so by the moderator. On more than one occasion, we have had people just "give up" on a defense, decide they want to quit, or, as intelligent mafia members, decide that they ought to close off debate by killing themselves immediately, e.g. directly after someone says, "I'm the angel and I found out that ... ." The death, of course, immediately ends the day. In order to punish this sort of thing, we have decided to let games continue even after a suicide-- the suicide is dead, but the round continues until a legitimate conviction.

Of course, you may wish to allow strategic suicides.