The gravitational potential energy of the International Space Station will be converted into other types of energy.
I would like to point out that the International Space Station also has a lot of kinetic energy too. Orbiting isn't hanging above the surface of Earth really high up. Orbiting is done by moving very fast. Basically, the ISS is traveling forward at 4.76 miles per second. Gravity is pulling it down. The combined forces result in the ISS following a curved, projectile motion path. That curve perfectly matches the curve of Earth. So, the ISS is technically forever falling without ever getting any closer to Earth.
In order for the ISS to actually begin falling more toward Earth, it will need to slow down. Let's assume that we magically stopped all forward motion of the ISS. Then it basically only has GPE. A lot of GPE. It's 249 miles up and weighs almost 500 tons. The GPE will immediately begin being converted to kinetic energy as the ISS begins to accelerate straight down. As the atmosphere thickens up, there is more friction on the ISS. The friction will begin heating the ISS, so now there is a thermal energy conversion happening. Eventually the ISS will get hot enough to ignite. Light energy has now been created too. Since the ISS is experiencing some atmosphere, there is a medium for sound to travel through. The hot, burning ball that is/was the ISS will be making noise, which is sound energy. That answers another question. Does a burning up space station make a sound if nobody is around to hear it? Yes. Yes it does.
All of the GPE will eventually be completely lost/converted when the remains of the ISS either impact Earth or burn up completely.