Has anyone had an old soap dry out or be otherwise unsuitable for its intended purpose and if so what did you do?
Depending on the soap, you can always try to rehydrate it. I have an old puck of Safari pressed into an Old Spice mug that's pretty dry. I always add a teaspoon or so full of water on top of the puck and let it sit for awhile, ideally overnight. The next morning I can lather it up and shave.