This is pure speculation, but I would hazard a guess of the early 30's. Assuming 230XXX was 1926, and they made about 20k after that, plus the Neu Modell, which as well all know was made in limited quantities, I would say that the worldwide economic downturn in the late 20s-30s likely claimed Dreyse/Rheinmetall as one of its victims.Hmmmm ...
Thing is that after Versailles Germany could not produce handguns in 9mm. The Dreyse was always .32 so they were well positioned to export from 1919 forward.
Do we know when they went out of business?