If you cannot see out of the door window (it usually contains a wide-angle viewer) then the Commander should be advised for entry in the Tech Log. The problem probably won't be fixed immediately, or even soon, but it might get fixed next time the a/c is in the hangar for maintenance.
As far as I'm aware, there is no specific requirement for the viewer to function in order for the aircraft to depart.
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Per Ardua Ad Ibiza