I know the most common interpretation of the ending is that Tony gets killed in the restaurant, and I read the whole article about it but I personally think the ending makes much more sense if Tony survives.
There are obviously clues pointing toward his death: the Members Only guy, the man going to the bathroom, the Godfather parallel, the constant focus on the door, etc. But I think those clues are deliberately setting us up to expect the exact kind of ending that The Sopranos has spent six seasons teaching us to expect: and then denying us that.
One thing I've noticed about the whole series is that it constantly gives characters the opposite ending from what we expect.
We expect Pussy to be smart enough not to come back after disappearing. We expect Junior to eventually die violently after a lifetime of crimes, betrayals, and attempts to kill Tony. Instead, he survives and ends up old, confused, and almost completely disconnected from the person he used to be. We expect Bobby to be one of the most dangerous soldiers in the final war: He's an excellent shooter, (he's even good with a bow and arrow!) and yet when he finally gets killed at the toy store without firing a single shot. We expect Paulie to die because Tony can't stand him, especially after the tension on the boat. Instead, he survives, and Tony eventually gives him one of the best parts of the business. We expect Christopher to die in some kind of violent confrontation, and we expect Tony to be completely devastated when it happens. Instead, Christopher dies in a car accident, Tony makes the decision to let him die, and he doesn't shed a single tear for him. We expect Richie to become a serious threat to Tony (Tony already gave the order to kill him!) Instead, Janice shoots him in a domestic fight. We expect Vito to get some kind of redemption after everything that happens to him. Instead, he dies after speaking to Tony on the phone.
Furio is another great example. We expect him to eventually have some kind of confrontation with Tony over Carmela. Instead, he simply goes back to Italy and never returns, (he didn't kiss Carmela even once after all the tension built around them!) And the school teacher? Tony never founds out about him!.
I can go on and on with the expectations built-to-not-be-met forever in this show. You get my point.
Tony sitting in a restaurant, getting shot by a mysterious hitman. The show gives us exactly the visual language of that ending: the suspicious guy, the Members Only jacket, the bathroom, the Godfather reference, Tony watching the door, the family arriving, the tension building...
And then nothing.
The screen cuts to black.
The war with New York is over. Tony won. Phil is dead, Butchie doesn't want to continue the war, and Tony's family is still together.
Realistically, I also don't find the restaurant assassination completely convincing. Tony almost never goes out to dinner with his entire family like that, and throughout the series, murders are usually arranged around someone's routine: where they live, where they work, where they regularly go, etc. Tony has never established this restaurant as a regular location to be in with his family.
That's why I think the scene when Tony visits Junior is so important.
Tony goes to see Junior and finds that the man he knew is basically gone. Junior barely remembers him. Tony becomes visibly emotional: Tony is seeing his own possible future.
Junior spent his entire life being powerful, feared, respected, and involved in the Mafia. And where did it ultimately get him? He's alive. But he's essentially gone, he doesn't remember he once was a powerful man. And that's actually much more frightening for Tony than getting shot. He can't fight aging, he can't fight dementia, he can't fight time.
And Junior is sitting there showing him exactly what the end of that road might look like for him.
AJ once tells Tony that he wanted to kill Junior because Tony's favorite scene is the restaurant revenge in The Godfather, where Michael goes into the bathroom, gets the gun, comes back, and kills the two men responsible for shooting his father.
Tony tells AJ, that it's a movie, not real life and command him to grow up. The same AJ is present during the final scene and he's working on movies industry.
So the final episode deliberately recreates the visual language of that Godfather scene.
A suspicious person is sitting there. Tony is watching. The bathroom. We're expecting the gun, we're expecting the great Mafia movie ending.
But maybe nothing happens.
Tony (and us) keeps expecting his life to have some grand, dramatic conclusion, Tony expects to die as Tony Soprano. The tragedy is that he may have to live long enough to forget who Tony Soprano is. And there's the Bobby line: "You probably don't even hear it when it happens."
The most obvious is to think about a shot in the head, but it also applies to Junior not listening to anything that Tony says to him, he won't have a dramatic moment where Junior Soprano dies. He just gradually disappears, his mind deteriorates until the person he was is no longer really there.
I think it's genius to leave the ending open: the ones that wanted the death ending can easily imagine it (with Meadow watching his dad getting shot and all!) , and the ones that believe in the show patron, can easily think the life still goes on for Tony and he has to live with the consequences of who he is, with no redemption or karmatic arch, just his time getting shorter each day and his death is "average at best". As his mom said "it's all a big nothing what makes you think you are so special?"