Up to now, one of the main points in Sopranos is that sociopaths like Tony and Silvio and near-psychopaths like Ralph, Jackie and Paulie live a life much better than the rest of us unless they stop playing by the rules of the game, in which case they are whacked. This despite the fact that they are lazy illiterate bastards whose only real interests are how much more they will "earn" and which broad will give them a blowjob each night. In view of this, I would think of two general types of ending.

1. "Godfather I" ending. Everything goes on roughly as in the previous seasons. Somebody in the organization cooperates with the feds, somebody gets indicted for relatively minor charges and the traitor is found and whacked. Some other guy thinks he is the rising star, he disrespects the bosses and gets whacked. Tony manages to survive all this and either remains the boss of the NJ crew or assigns somebody else as the leader and retires - in the latter case, Melfi is happy. This ending is realistic and consistent with history. After all, most of the crime family leaders died outside jail, while organized crime only gets more organized as time goes on.

2. "Goodfellas" ending. The whole thing breaks down. Somebody high-ranking in the organization, even Tony himself, gets trapped by the feds, flips to save himself and his family and talk his brains out. All codes break down and everybody reveals what a selfish and scared bastard he really is when he has nobody to protect him. Tony's pathetic family begins to realize where their classy lifestyle is really based on. With Tony and his crew facing the electric chair or life sentences, everybody ends up with a different view of life in general. This ending has the moral that crime never pays, but it is also less realistic than the previous one. Another problem is that, with this ending, a possible next season or a film sequel are out of the question.

Of course, there are many other options in between these two.