This bug has happened to me before as well, the best solution at the moment is to remember to put the belt back on after death.
The items are stored in a separate file, but since you got an internal server error as you swapped the hotbars, they were probably lost. The only way they could be recovered would be a rollback, which I assume would not be done under the no refunds policy.
Actually, you could try making a new belt and hitting b again. It should return anything that was stored, but the wand is probably lost. Won't hurt to try though, since the cost is so low.
