Is it even possible to keep someone "on hold" forever? My experience (in Poland) was that it'll take at most 20-30 minutes before something somewhere timeouts and the call gets disconnected.
Try calling the assurance maladie in France :) I gave up after about 80 minutes of their little silly jingle while the agent was allegedly looking for the answer to my problem.
I've been on hold for 4+ hours when dealing with the California government. The only timeout there is at the end of the business day, when it will automatically hang up.