Really? We're blaming Brexit for this? I'd say the lack of direction and focus, complex fleet structures, trying to everything: a network carrier, a full service airline, short haul, long haul, regional, low cost. It had a ghastly cost base and was rapidly coming irrelevant. For many years it has been problematic. Brexit has been a recent phenomena - nobody expected it to happen so until the referendum dare had zero impact. Now that it's happened it will have the most minuscule impact on Air Berlin that it's not worth even mentioning.
I missed my bus this morning. Damned Brexit!