Is there any where to predict it without thawing? In terms of measuring it. What if the body was immersed in sugar prior to freezing?
Take a look at the frozen carcasses of mammoths and dire wolves found in the permafrost regions of Siberia... Freezer burn happens quite frequently... the outer layers of soft tissue will start drying out.
If this is true or not... A mammal carcass preserved at -20 degrees can last long... very long.
I recently thawed a crocodile, which was frozen at -20 degrees since 1986... Except some freezer burn and shrinkage of the meat within the hard and partly ossified skin, you wouldn't even think that it was frozen for such a long time.
Adding sugar decreases the freezing temperature of water and the freezing process will take longer. Given the fact, that you have -20 degrees during this step, too - nothing will happen with the carcass.
So: no rotting, no necrosis, but: long time freezer burn