These are really difficult situations. Assuming you shut the engine off when the light came on (as opposed to driving it until it quit running), what will most likely happen is they’ll put in a new plug, fill it up with oil and send you on your merry way with no apparent problems.
But the prolonged running with very low oil and the brief running with no oil certainly caused some internal engine damage-- it’s just a question of whether that damage will manifest itself during the expected lifespan of the car. But what happens if the engine starts burning tons of oil years from now and eventually dies prematurely? It’s becomes very difficult to hang something like that on a single incident with so much time between the incident and the damage, even if it was almost certainly the main contributing factor. In some ways it can almost be better if you do run the thing 'till it dies in these situations. You’ve also got the ethical consideration of whether you can sell the car without disclosing this to buyers.
With any of these situations, be absolutely sure you get as much documented in writing as you can. It might have been better if you’d had it towed to an independent mechanic, but a missing oil plug should be obvious enough that even getting something in writing from the tow truck driver might do. If the car appears to be okay, you might even be able to get the dealer to write you a brief description of what happened (might as well get it notarized since you’re at a dealership anyways). That way, if the car takes a dive sooner rather than later you might still have some recourse against them. Before you do anything else, it might be worth consulting with a lawyer about the best way to document the incident or any other steps that might be helpful.