I have had the crew oxygen supply drop to zero pressure, and opted to descend to 25000 feet. My reasoning then (and would still be) that TUC at 25000 feet is approximately 4 minutes, and an emergency descent to 10000 feet could be accomplished in 3 of those 4 minutes.
Whilst there may be debate upon my reasoning stated here, I think that there is no argument that a depressurisation at 41000 feet or even 31000 feet without oxygen being available would be CERTAIN death.
On the occasion that it happened to me we were fortunately operating a short 2 hour sector, and increased fuel useage was not a problem. There was sufficient fuel to continue to destination. Long sectors, e.g. trans Pacific, would cause a much greater fuel penalty, perhaps making it impossible to reach the destination, but bear in mind that we must always carry sufficient fuel to cover depressurisation at any point en-route, and a diversion to an en-route contingency airport may be necessary. (I do not refer to ETOPS operations here, but ALL operations).
In my mind, continued flight above 25000 feet without oxygen being available is a totally unacceptable risk, and a loss of crew oxygen warrants an immediate descent to a lower more suitable level.
Regards,
Old Smokey