The existence of Mozart's music is almost a promise that the loss is not irretrievable. The world to which it refers and out of which it comes really does exist. As it preceded us, it will follow us. The sense of loss behind is also a sense of hope ahead. This is why Mozart's mention of death as man's true best friend is not morbid.
Death is our means to completion.
It is hard to believe that there could have been more. Miracle is the exact word used by Goethe and by other agnostics and unbelievers in reference to Mozart while he was alive and shortly after he died. We are mere mortals eavesdropping.