I am sorry to hear your are worried about Dante. I am a veterinarian and will do my best to help.
Is he taking any pain medication? Panting at night can be a sign of pain.
Drinking a lot of water can indicate kidney disease (which should show up on the blood tests that were done), Cushing's disease (which requires special tests), a bladder infection (a urinalysis would find this, not blood tests).
He might be near the end of his time. If he were my own dog, I would start pain and anti inflammatory medication and do a urinalysis to look for something easily treated, like a bladder infection. If the urine test was normal, and pain medication like carprofen, tramadol, and/or gabapentin did not help him, then I might consider letting him go.
Is he eating? Dying dogs, suffering dog, slow down or stop eating. If he still has an appetite, he may not be ready to go yet.
Let me know what other questions you have and how he is doing. Rebecca