huiiii!!!Well, I didn't expect this to work out but apparently it's possible to change from a train in Gare du Nord to a train in Paris Austerlitz in 18min under optimal conditions (maybe even 17min with lighter/less luggage).
Thank you DB for giving me this challenge! 😝
(But the main thank you goes to the extremely friendly and helpful Eurostar staff who already booked me a hotel although the delay and the potential missed night train was not their fault!)