Jupiter wasn't my bird, my wife is pretty upset she loved that bird and while I wasn't as attached to him as she was I did enjoy the love he showed her. Mars is still healthy for now. As far as the Necropsy I don't know enough about what they look like inside to be successful. I have been studying but only had a couple months I couldn't find the books until recently.
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.
I suspect stroke or heart attack, he was far less trouble than Mars she gets into everything. They had both followed us down to the work shop, Jupiter was strutting around the shop hadn't pecked at anything bumped into a tool cart with his wing and fell over.
My wife was out with our daughter enjoying the 4+ feet of snow we have when it happened. I was maybe 5 feet away from him, talking to my mother helping her with a break job on her truck heard him hit the cart turned around to see him stumble and fall