I don't know if it is such an easy answer. On the one hand, a policy of not prosecuting the office holder might help the peaceful transfer of power; on the othe

I don't know if it is such an easy answer. On the one hand, a policy of not prosecuting the office holder might help the peaceful transfer of power; on the other, such a policy creates an unaccountable sovereign every four years. Was it fear of prosecution that kept Caesar from giving up imperium when returning from Gaul? It was certainly a factor. Would there have been no Roman civil war if there was such a non-prosecution policy in place? I'm less certain. The risk you bring up must be carefully considered, but so is having an unaccountable sovereign, just four years at a time.