+++UPDATE 09 OCT: Air Berlin today announced it will cease all operations effective 28th of October 2017. Flights operated by Niki (HG airline code) are not affected.
04 September 2017: Bankrupt Airberlin today announced that ALL long-haul (i.e. inter-continental) flights to and from Berlin will be cancelled from the 25th of September.
As far as Düsseldorf is concerned all but the long-haul flights from and to Boston and Orlando will be continued into October.
Yesterday (03 September) 60% of Airberlin's intra-European services were cancelled for no further reason other than "operational" ones.
Please do not book nor count on Airberlin any longer. Eurowings offer reliable budget direct long-haul services to Germany, so does Condor.
Update 25 September: Effective 15 October ALL long-haul flights are cancelled as leasing companies want their Airbus 330s back.