Translation:I worry that they are never coming back.
I tried this: "I worry about the fact that they are never coming back" but it was not accepted. The norwegian "over" seems to me closer to "about" than "that".
I think it is rather because you had to include "the fact" to make your about work. In my dialect I would prefer bekymre over uroe Jeg bekymrer meg for at de aldri kommer tilbake. The translation stays the same