The airport website confirms the temporary closure of the Air Berlin Lounge (C gates):
https://www.dus.com/en/services/lounges .
However, the Open Sky Lounge is still listed as open. But I don't know if (eligible) AB pax are admitted? The Oneworld website isn't listing the Open Sky Lounge at all (but still lists the now closed AB lounge).
Hugo Junkers Lounge (near B gates, Schengen) is still listed for all Oneworld airlines departing from B gates, including AB.
Also the Etihad Website now refers all pax to the B gate Hugo Junkers Lounge.