If Watson wins, it should have to keep coming back as defending champion until someone else beats it. It should also qualify to return in the Tournament of Champions if it gets that far.
It would be quite entertaining, but that would mean either more permanently moving Jeopardy! filming to IBM's campus (cost prohibitive) or rebuilding Watson on Jeopardy!'s set (also cost prohibitive) and you see why this is just a three day exhibition match.
Does anyone know what these IBM supercomputers ultimately are used for after they're done winning Jeopardy or beating Gary Kasparov? I'd imagine something top-secret for the US government, but it would be nice to know exactly what Deep Blue is doing now.
Now that would be a true test.