I'm sorry to hear this =(. He was definitely in rough shape when you posted earlier. It looked like he was well fed and cared for so whatever caused his death was likely some kind of system failure or possibly a tumor as Tracie mentioned. It's hard to say for sure without having a necropsy done.
I think you'll find another dragon is a start of a completely new adventure. You'll never forget Miki-moto and I don't think you'll see a new dragon as a replacement either.
If you would like me to review your setup and lighting to make sure everything is just right for your new friend, I'll be happy to do so. Just start a new thread in the enclosures section if you'd like.
One thing that really jumped out at me was the OP stated the dragon smelled like eggs. Egg smell is usually caused by sulfur. So then I found this:
When globulin begins to decay, a toxic chemical is released that's called hydrogen sulfide, which has that very potent sulfur smell. ... Both of these proteins release that sulfurous smell, resulting in an odor that immediately tells you that this egg has gone bad.
So, it would seem there was some type of organ failure that was causing the proteins in his blood to decay causing the the sulfuric smell.
I’m no scientist, but my daughter is.
OP: Sorry about your beautiful friend. He looks like he was treated well and you did a lot of investigating to try to resolve his issue. Keep us up to date with your new scale baby.
I am sorry for your loss, that is so rough.
No other dragon will replace him ever but you will find it in your heart to love another one
again.
Definitely let Cooper run over your setup with you, if you need more help!