Gone to Pot
The earliest usage, which goes back at least to the sixteenth century, seems to have been literal, actually going into the pot, chopped up into pieces as meat, for stewing in a pot. A number of writers use the phrase with allusion to death, in some instances with the implication that the person dying had been the victim of a cannibalistic feast.
A Hog on Ice by Charles Earle Funk, 1948.