as pointed out, it is helpful to have one if you have a qualified vet to do it and the money. I had one done on Luna for $120(I am sure it will vary somewhat depending on where you live). She had health issues and I really wanted to know what had happened.
If you post her setup, supplementation, feeders, gutload, lighting, water, humidity, etc. some forum members may see some other problem. Not that you can get a definite answer from us, but a little troubleshooting can't hurt especially if you think you will get another.
That said...I am very sorry this has happened to. I lost my Luna last summer and it was almost 9 months before I got another. Many of us have had this loss and the support of this forum can be a great resource.
lele
p.s. if you decide on a necropsy try to get an ARAV certified vet to do it. Go to link below for a link to state listings.
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Chameleon Help & Resource Info
1.0 Nosy Be Panther Chameleon - Cyrus
0.1 Veiled Chameleon - Luna. She's now hanging from her big jungle gym in the sky
1.0 Beardie - Darwin
1.1.1 Side-blotched lizards - Ana and Stan and Stan Jr.! 
0.2 felines - Kyndra and Lita
0.1 African Clawed Frog - Skippy
0.1 Chilean Rose Hair Tarantula - Rosa Leigh, Died 4/21/06 
0.1 Goliath Bird-Eater Tarantula - Natasha, donated to science 4/4/06
?.? Pinktoe Tarantula - no name yet