It's a poor question.
Strictly speaking, potential energy is not conserved. Potential energy can become kinetic energy as it does when a ball falls toward the ground. Likewise, the potential energy will increase as thrown ball moves up away from the ground.
Could a collision happen while an object is in free-fall? Yes, of course. The potential energy of the system is changing the entire time. The collision really had nothing to do with the gravitational potential energy. Considering this example, it's difficult to understand what the question is trying to ask. But the easy answer is, "No, potential energy is not always conserved."