I am so sorry to hear about Dozer. My sincere condolences for your loss, after doing all you could have done for him.
My name is Rebecca. I am a veterinarian and will do my best to help.
GDV is the worst and most urgent of all the emergencies we see. If his stomach was dead, devitalized from lack of blood supply, that trauma probably happened before surgery. The twisting of the stomach that occurs with bloat pinches off the blood vessels to and from the stomach, and then the muscle and other layers of the stomach die. Even if the stomach looked good at the time of surgery, enough damage had already been done that the stomach could not recover even with the blood supply was restored; it had probably been deprived of oxygen for too long.
With his blood not clotting, it sounds like he developed DIC (disseminated intravascular coagulation), an abnormality of the clotting system that can occur following many serious illnesses and conditions and DIC is almost always fatal. You made the right decision to send him to heaven and not do a second surgery.
Even though you got him to surgery so quickly, it sounds like it was already too late. The stomach's blood supply must have already been compromised past the point of recovery.
Please accept my sincere sympathy and let me know what other questions I can answer.