For the attention of Intruder, no-one flying the Atlantic should be flying "blind" in any case - that's why all proficent operators will have not only the closest alternate airport pre-programmed in their FMS, but also the approach in use, for the conditions reported.
Most Atlantic crossings these days are performed by Aircraft operating under ETOPS constraints, one of which is the carriage of fuel for the (hopefully) hypothetically implausable "critical fuel scenario".
Therefore, a descent to 10,000 ft, in the event of a loss of cockpit O2, over the Atlantic, and obvious diversion, to repair , is the only course of action I could consider.
