What if Tommy had rejected the Mafia?
At the start of the game, Tommy is a taxi driver. A dead end job with low pay, then all of a sudden while he is on a break he is forced to drive Sam and Paulie to safety. We see him with the money and refusing to co-operate with the Mafia (he says "It's better to be poor and alive than rich and dead"). After he goes back to work and after picking up some more fares he is attacked by Morello's men and he goes to Saleri's for help. After this his contract is terminated with the taxi company and Tommy decides to join the Mafia. And then the main story begins.
Why did Tommy join the Mafia after his initial reluctance to join them? Why did he not think "Lost Heaven is too dangerous for me" and leave the city as soon as possible? He could have moved to the other side of the country (like he does at the end of the game). That way he would have lived and not ended up being shot on his own front lawn.
It does sound stupid because if he had left Lost Heaven after mission 2 then we wouldn't have had a game (and he wouldn't have met his future wife and had a daughter) but Tommy could have lived for longer had he have stuck to his original intentions and rejected the Mafia.