Maybe a vet could do a necropsy, or somebody who is very familiar with the inside of a turkey. I'm very sorry to hear about this. I have no experience with turkeys and very little with chickens but I had a chicken suddenly die this summer. And I have heard from people that they have literally seen their chicken just drop dead right in front of them for no apparent reason either. So you have to assume it's either something like a heart attack or a stroke. Or maybe a blood clot in the lungs. But who knows. Maybe we should all be so lucky just to go like that, happy one minute and gone the next. But it's still very hard. Very sorry.