That wound is not sufficient by itself to have killed the fish. Were there any signs or symptoms prior to the death? Flashing, breaching, clamping, isolating,.....
As Cindy says, we would like to have the complete water chemistry. Water is the lifeline for the fish and in good water healing is more the norm than death. It is much cheaper and easier to correct water issues than to treat parasites and bacterial issues.
Zone 7 A/B
Keep your words sweet. You never know when you may have to eat them.
Richard