I'm so sorry for your unexpected, horrible loss.
I've never owned a ferret but I can relate to the pain of losing someone you loved so unexpectedly. My first horse died back on November 21, of a suspected guttural pouch infection and after seven hours on IV fluids, she never showed any symptoms, which the vet said was typical of the infection. The night before was her first night back in the arena after a leg injury and she was her happy go lucky self as she trotted around the ring. I can only imagine how you're feeling right now, because I still shed tears for Indie.