The Harpoons are used up too. We're confusing the weapon with the launch platform.
I'm strictly a surface guy, but I have never heard of a Predator being outfitted with Harpoons, let alone two of the suckers! That would be a hell of a dramatic boost in their capabilities.
The Predator B (Reaper) is a bigger version of the original Predator. It has a payload capacity of 3000 lbs, and its two inner hardpoints that can handle 1500 pounds each. The air-launched Harpoon is 1144 lbs, so in theory the Reaper should be able to carry it. Whether they have compatible mountings is another story. I also don't know if the length would be an issue.
I personally think it would be rather interesting configuration.