If someone this is happening to can check to see if their AC compressor is not spinning, that would be a sign that this is the culprit. Every vehicle I'm aware of is designed to stop the compressor spinning when it's out of refrigerant as refrigerant is what lubricates the compressor.
If it is, then run to the auto parts store, grab a cheapo can of refrigerant, and charge it up to see if it works again. If it does (assuming the leak is slow and not a giant hole somewhere), then you know what's up.
This all, of course, applies to someone who lives a decent distance from a dealer. If you are right near one, it's their problem.
