No, this is not a stupid question. In fact, there are no stupid questions; just rhetorical ones. Generally speaking, paddles are going to float if you accidentally drop them in the water. However, if the paddle is not sealed completely and water manages to seep through then it could end up sinking. But, most of them are constructed with quality in mind and will float. There is only one sure way to be 100 percent positive, though, and that is to drop one in shallow water to see if it will sink. This way, if it sinks you can easily pick it up from the bottom of the water.
If there ever comes a time where you are paranoid that you will lose one of them, you could also strap one to your wrist. Though, this could complicate things when you want to switch hands. Honestly, this is not an issue you will have to deal with frequently so just be sure that they float.