"The firm said in a memo to pilots that its bases at Berlin Tegel and Dusseldorf airports were also at risk of closure by the end of the summer"


That's slightly disingenuous; Berlin-Tegel is closing permanently on November 8th, 2020, which is only a matter of days after the end of the "summer" season. As such, the base in Berlin-Tegel has to close. The new Berlin-Brandenburg airport will officially open on October 31st, with flights progressively moving from both TXL and SXF to BER over the subsequent days.