My wife recently took our 2003 FX45 (50,000 miles) to the local dealer for an oil change. Three weeks and 1000 miles later, the car began making noise and the warning light appeared. Wisely, my wife parked the care asap and had the oil checked. No oil appeared on the dipstick. So, she calle the dealership and had a service tech come to look at the car. After putting 5 quarts of oil in the car, he suggested she drive it a while and see if it keeps the oil in the engine. Otherwise, he told her, you may have severe engine trouble.
Now, the valves are tapping loudly. They weren't tapping at all before. The oil didn't leak out of the engine, nor did the engine show any signs of burning the oil? It seems likely to me that the dealership forgot to put oil in the engine when the changed the oil. How much damage could this have caused and how should I proceed in having them make this right?

You should for sure tell them to make it right regardless. Most of the times when oil isnt put in, the engine will completly fry. See if they will get you a new engine