I think you better call a couple pool places in your area. The bottom looks like concrete and it could be or it could be a standard pool bottom which will let water thru. The metal walls are to hold the liner. If your pool has a liner it will not hold water without one. If it didn't need a liner there would water in it. The only thing that worries me it the pool walls moving without the water. You could make wooden braces with plywood and 2x4's to support the walls from moving
Another possible solution... Using a large tarp, to act as temp. liner for the winter, would hold the water in, keep the walls up, and hopefully save my pool. Any Thoughts?