Hi again!
I'm happy to report that the plant has recovered beyond all my expectations! (for scale, the stainless steel disc is 60cm in diameter and the glass jar is a 3L pickle jar)
I'm starting to suspect that letting the roots dry out causes much more damage faster than overwatering. Right now I have some roots living in the water on the saucer under the pot without any issues, but once I drain the saucer, they'll end up dead in a day.
Overwatering has been discussed in this forum and everywhere a lot, would be interesting to read up on underwatering to see if my suspicions are true.