Our Airbuses (A300) have 2 flight deck oxygen bottles with a crossfeed system so that 3 masks are fed from one bottle and 2 masks from the other.
If one bottle had leaked to empty then selecting crossfeed might empty the other if the leak was downstream of the selector valve. We also have a portable bottle on the flight deck so, if after selecting crossfeed, a leak was identified, then I would go back to normal feed and have the portable set available should it be required.
I'm not sure what the later Airbuses have.
Hope this helps.