O2-mask: not under European law.
Alone on the flight deck: has been prohibited in most airlines since this Lubitz-bonker crashed the Germanwings Airbus, because he could not take life anymore.
It's always a few idiots who ruin it for the rest and at the same time it is the legislators who rush to implement new regulations/laws, just because something went awfully wrong on one single flight out of hundreds of thousands. What a mad world full of people only interested in covering their own behinds.