The most likely ending, in my opinion, was that the audience was whacked. This can't really be disproved, and follows precisely what Bobby said on the fishing boat.
This leaves two questions. the first is whether Tony was killed by the M.O.G., or whether "life goes on," and Tony remains the same sociopathic degenerate monster, his wife remains a horrible woman, AJ continues to disappoint, and Meadow continues her reasonable success.
I think that there are valid arguments for both, but what I believe Chase wanted us to think is that Tony was likely killed then, and, before he was killed, his personality and actions were so that he would never change.
There are plenty of indications that Chase wants us to think Tony was whacked. The two African American men in the Holstens (representing the original failed assassins in Season One), the P.O.V. argument, the bathroom / Godfather reference, the fact that the M.O.G. does not order anything, or sit down for more than a minute, but simply eyes up Tony, and then enters the bathroom, probably for a position for a clear shot.
The Bobby speech on the boat (and its subsequent reflection in the penultimate episode) also strengthen this theory that Tony was likely shot in front of his horrible wife. There is also the fact that Tony has murdered, exploited, maimed, and ripped off hundreds of people, all of who have motive.
The theory that Tony lived on as his sociopathic self is also credible. However, I believe that Chase wanted to tell us that Tony will never change, and also kill him. Why not? The Journey song, in my eyes, says that Tony has chosen the life of a Boss, and he has lived it so long that he will never change. Then he is killed. An ending that he thought would happen (that, or jail). Chase has repeatedly made clear that these men almost always die in a brutal, undignified way (Tony B, Phil S, Vito S, Dickie M etc).
To summarize: The audience was whacked, as was Tony, who had chosen his path in life, knew the risks, and finally got his comeuppance, in front of his family, in the side of the head.
Just my 2 cents:)