GTA Vice City question: When have I beaten the game?

ok so me and my sister are playing GTA: VC. the mission is the one at Diaz's (i think) old mansion where Lance turns on you and you have to kill him. is that the last mission in the game? i killed him and completed the mission, then sonny talked to me and credits rolled and it seemed to be over. however, when i stopped the credits, it gave me 30000 for passing the mission and i continue to get cell phone calls. however, all of the calls are mostly congratulations and don't lead to missions. there's are no new missions to do it seems and no new property available to lead to missions.

i say we've beaten the game (although we is more her as my sister plays the most and did most of the missions) but my sister says that we're still supposed to kill cortez and it ends on his boat or something.

so basically, is the game over? does tommy not care about getting his money back from cortez? and if not, then where are the new missions supposed to come from? hopefully someone takes pity and gives me an answer.

i don't feel like driving around the city for hours to find a mission if it isn't there. plus, this will free me up to go on killing spree after killing spree if it is over.

 

thank you very much.

damn this site rules. ask anything and get an answer in no time.