Patrick can you give us a few details?
You say 'lost it's height', does that mean height at all four corners, just the front or just the rear?? Frankly, it would be odd to be low all around. I assume it is now in a garage, is that correct. I'm sure it has been started, but has the car been moved? If the car is low, just starting the car will generally not level it. The car must be moved. For instance, sometimes when we raise an X350 then put it back on the ground, one end is too low. When we start the car and drive it out of the building, it levels itself before we get to the street. Granted that "shouldn't" happen; but it does occasionally. Even when it does happen, rarely does it repeat such that the owner notices any issue. By the same token, suspension settling while in storage can occur as well.
So, see if moving the car will allow it to level normally. If it does, the next step would be to monitor it and see if it happens again right away. If it still falls, then a leak should be investigated.
Your friend could investigate a changeover, but I would want to find out if it was another fluke this year, or a real problem. Then assess the repair and make a decision based on that.
Good luck!