From Grand Theft Wiki
Sayonara Salvatore is a Grand Theft Auto III mission.
This is the first mission Claude can take up with Yakuza leader Asuka. During the cutscene, Asuka informs Claude that in order to show that all ties are broken with the mafia he must assasinate Don Salvatore Leone. This mission can be done several ways but the easiest way in completing the assasination is going to the rooftop adjacent to Sex Club Seven, taking out your Sniper Rifle, and then aim and fire. This mission is still the last mission that features any member of the Leone Family Mafia, as no other character is seen or heard from again (aside Toni who can be heard complaning about his mom on Chatterbox FM).