Oxygen burns. Without oxygen the soft tissue would and could last forever; or until the end of the earth, whichever comes sooner.
Phooey, anaerobic bacteria would digest it in a heartbeat. The conditions must been really acid, basic or cold for it to last ansd somewhere the guy got autoclaved, preserving the tissue.
Could happen, I guess.
P.S., Oxygen doesn't burn. I take it's been a long time since you took Chemistry.