oh my
An aircraft "full" of oxygen because the masks have dropped. That blows Avogadro's hypothesis out of the window faster than that fat red-haired bloke in the Bond movie. Actually may I remind you of the Boeing advisory of 01 Apr in such situations that depressurisation to extinguish a fire must be accompanied by jettisoning ALL fuel including contingency and landing reserves so as to deprive the seat of the fire of both oxygen and fuel. Under the circumstances CFIT Regulations apply and it is not necessary to land at the nearest or any airport.
Raoul Lufbery (WW1) said that if his aircraft caught fire, he would put it into a steep dive and if that did not work, he'd jump. It didn't and he did. Clarence A Maaske (WW2) said that depressurisation didn't lose enough oxygen to suppress the fire but it stopped the screaming. (Lufbery flew a single seater, Maaske a Superfortress).
Lovely idea to depress but i don't think it is going to happen fast enough to make ten cents difference. Just point the nose at Johnnie Howard's house and hope he is in.