The highway code and case law is quite clear on the matter. Motorists are required to take the road as they find it.
We are not obliged to take extraordinary action in the event of an unplanned failure. 7019’s are futile and, for any lengthy period of inoperation, pretty useless as they tend to fall off.
Its fairly obvious the lights are out, so why do we need a sign? Its a bit like the endless miles of “FOG” warning signs on motorways when you can only see 30ft in front!