There's a ton of theories on tinternet. I agree the first time I saw it we jumped up thinking the telly had packed up.
Then the credits rolled.
Bacically make of it what you will.
Was Tony killed by the guy who went into the bathroom? If so who was he? New York?The Russians? What was all the palaver with Meadow parking about? Just to build suspense? Or to delay her entry until the guy emerges from the bathroom and she gets shot accidently?
Or does nothing happen in the restaurant ? Does Tony just carry on feeling paranoid for the rest of his life? etc. etc..
Personally , for me , nothing happened . Tony wasn't shot because David Chase didn't write him being shot.
The programme just ended pretty much as it began , we just got a eight year slice of their lives.