The good news here is there's probably little chance of engine damage----needless to say though that's one very dangerous condition. Discovering it so late is scary and will certainly serve as a reminder to check vital fluids every other fuel tank fill up.
Another vital bit of info maybe needing frequent reminder is the stock dash gauge for "oil pressure" is NOT a reliable indicator of anything----nothing! It doesn't measure pressure rise or fall, only registers if oil pressure between 7-15 PSI is present at the sending unit. In theory as little as 2 quarts could be circulating and that gauge reading "normal". Should that gauge ever fall during normal engine operation its very possible engine damage could be experienced in a short time because by then little to almost no oil flow was present.
With the too many horror stories coming from the quicky lube outfits I'm a bit shocked those who read and participate in SMB forums or other similar sites patronize them. I get the ease of driving in and having someone else do this semi-dirty task but given the risks those outfits pose I'm happy to spend the time and get a bit dirty.