hmmm. I guess I would ask the restaurant whether it was going to do anything and if no then I would leave without paying except for a small tip for the wait staff.
Bingo! You have it nailed right there.
I left a restaurant once after talking to the manager. He allowed a group of non English speaking illegal aliens in to go from table to table to sell their stupid flowers. Peeved me to no end to be disrupted twice while having drinks before dinner. There was 4 of us. We pd the bar tab and left.
I would start with throwing food at them, or maybe a hot cup of coffee in the lap. A nudge, and elbow to the head, and a few choice words under the normal din of the background chatter...but I would not let this go unchallenged.