I will be heading to Paris in September, so I will be able to confirm then, but here is what I know about the Duplay house.

The house was rebuilt in the 19th century because the original building wasn't strong enough to carry the weight of the extra floors. However, the reconstructed building followed the original floor plan.

The courtyard is still there, you enter it from a little alley off the Rue St Honoré and anyone can go into the courtyard. There had been a restaurant called Le Robespierre there for many years, though it is now closed, in what used to be the Duplay's living room. I don't know what is there now. As of the 1950s the separate door was still there, though it opened onto a storage closet. If it's got a preservation order then hopefully it's still there.