If you have a fire, depressurizing is a normal procedure in many cargo aircraft since there is no fire protection system on the main deck. 777 freighter has this procedure. The problem off course with passengers is that you automatically activate the passenger oxygen system and re-establish oxygen generation on the main deck, which is exactly what you are trying to avoid.
As far as the different flightplans work: a different flightplan could very will have "survived" on route 2 when there has never really been a complete shutdown (it might be removed if you change the databases during preflight, I'm not sure, but that happens not very frequent...). But activating a flightplan on the other route 2 page pretty quickly can lead to "not on intercept heading" if I recall quickly. So I don't really consider it something that can happen "by accident".