bribed FM's in cities die next turn

[Gaius Sempronius Gracchus]

is this normal? for example, Hiero of Syracuse was bribed and I was quite excited to end the conflict peacefully and to have Hiero as an FM, but the next turn he died a 'heroic death in combat'. This goes for the FM in Massila, Byzantion, any independant city that has an FM in it.

is there a way to prevent this? moving them out of the city doesn't help either

I was just about to post almost exactly the same problem. As the Sabyn I noted that the governor of Sabata was Disloyal, so I succesfully bribed him and then.... as you noted, he died the next turn - an Heroic death. Very annoying.