Depends on how much air gets to the cadaver, doesn’t it? (Correct me if I’m incorrect, smarter folks.) Concrete certainly isn’t airtight, neither is a gold encasement most likely. Worms, bacteria, water, all kinds of fun creatures and elements are likely able to get in, so the look may well be accurate by now.
Yeah I think in general this would be on the milder end of the spectrum. Also the reason I found that answer is because I guess people were claiming to have his cremated remains in jewelry. I didn’t actually read the article since google just summarizes it but I bet people were selling them.