There is an interpretation posted on Wikipedia that supports my ambiguous ending theory:
Spoiler Below The ending is said to offer no closure or catharsis for viewers. Instead, it is left open ended allowing for the viewer's own interpretation.
The family may go on living their lives normally, as symbolized by the use of Journey's song "Don't Stop Believin'": "And the movie never ends/It goes on and on and on," or the family may have been killed, as symbolized by the abrupt ending. The final scene is described as:
"Tony is the first to arrive at Holsten's for a family dinner. He sits in a booth and plays a song on the jukebox, watching the door. Carmela enters and joins him, asking about his meeting with Mink. He tells her Carlo's gonna testify and she takes the news with a sigh. AJ arrives next, complaining about the more mundane tasks of his job but quotes old advice from his father: "Try to remember the times that were good." Meanwhile, Meadow struggles to parallel park outside. Customers come and go - a shady looking guy who's been sitting at the counter enters the restroom. Finally parking the car, Meadow runs inside to join her family, just in time for dinner."
It appears that the intention of the creators was for viewers to interpret the final scene individually. Interpretations have varied from Tony being shot to his future indictment or a possible deal with the FBI. In the previous episode, Tony recalls a scene in a boat with Bobby whereby the men discuss death and Bobby comments that one will never know when it happens. It may be the case that the final, confusing, blank at the end of program signifies Tony's death. However, there is no way to determine the significance of the blank screen at the end as any interpretation is conjecture.