It doesn't matter what happened, we know what will happen to Tony in the end... he'll either be killed or in jail, he said it himself.
There's no one who wants to kill Tony in that moment, so the guy in the jacket acting on his own orders or following an unseen boss doesn't make a lot of sense. We also get plenty of foreshadowing about Tony's possible death, specifically with saying when you're whacked it's very quick. But this show also hasn't been afraid to show us everything. We know about Tony's enemies, about the FBI, about every detail of his life... so why not show him getting killed?
If people really think about it, they shouldn't be shocked at this kind of ambiguous ending. This show featured dream sequences and symbolism VERY heavily and we were rarely given what we expected. Alan Sepinwall wrote about it
"Every cooperating witness would die before they could provide anything of value to the FBI... Before Richie Aprile can go to war with Tony, Janice murders him over a punch in the face. Melfi never tells Tony about her rapist. Furio runs back to Italy. And still people expected a familiar narrative."
and he's exactly right. So to expect a resolute ending wasn't fair from the show.
I think it was a bold move and one that you probably won't see again because of the divisive reaction.. and for that reason, I loved it.
The AV Club has a great article on the finale too..
http://www.avclub.com/articles/made-in-america,89671/
Maybe he dies at the end of “Made In America,” when the Members Only jacket guy puts a bullet in the back of his head (something we don’t see, because we cut to black from his point-of-view). Maybe he dies in 40 years, surrounded by family and friends and little Parisi grandchildren. (At the thought of that, maybe he would have preferred the bullet.) Maybe he dies right after leaving Holstens when he gets hit by a bus. Maybe he dies because he gets cancer. Maybe the cancer is eating him alive right now. Maybe he dies in a fight with Carmela, when she finally gets fed up and takes a shot at him. Maybe he decays slowly in a hospital somewhere, like Uncle Junior, the only solace he has a moment to look out the window at the sun and the birds, a moment to wonder who he is or who he was. Tony Soprano dies. So do you. So do I.
So what does Chase leave us with when he wants to get us to contemplate the whole series? He leaves us with a man looking up at a door to see who’s entering a restaurant, then a black screen. He leaves us with almost unbearable tension, which he then doesn’t allow to dissipate. He leaves us with a blank space into which we can project whatever ending we want. The “Tony dies!” argument again reduces this to essentially one possible reading: because Tony rejected the lessons of his trip to Purgatory, he now will suffer for his sins. Does Chase really want to tell us this? Does he really want to leave us with something that boils down to “crime doesn’t pay”? I don’t think it’s really in keeping with his modus operandi, to be honest.
But, also, we aren’t dead yet. There’s still time to reach out and experience all of the things you’ve missed, to make the most of every moment, to remember the good things. Tony Soprano blinks out, so his time, at least in our terms, is done. But we have this moment and this lifetime, and it will be gone before we know it. What comes after is anybody’s guess, but what we have now is something none of us experience in its fullness every day. The things that seem like they matter often don’t, and the things we lose ourselves in are often the least helpful. Chase leaves us with nothing but the blackness, and he’s giving us space to think, ponder, and consider, not a puzzle to be solved. Embrace the mystery. You’re not dead yet. What are you gonna do about that?
I don't think it matters if he lives or dies... and that's the show's version of closure. He met with Junior the scene before and that was another glimpse into Tony's future. We know what could happen to Tony, so why do we need to see it? He could be killed, he could be arrested and die in jail, or the third option... he could live but as a senile, old man who is just a shell of his former self. No matter what, we know one of the ways Tony will end. He's not going to go straight and live a good life... he's not going to become the biggest boss of all-time (and if he does he'll still either end up in jail or dead). He's just going to keep on living, however that happens.
I don't think it's fair that so many take a negative view of the entire series because of the final scene. We're really going to forget
EVERYTHING? All past episodes and plots are now tainted? Nah, that's just people being disappointed they didn't get what
they wanted from the show in the end. The Sopranos is still one of the best shows of all-time, many would say 2nd behind The Wire and that's still completely justified despite the ending.