Thank you very much! Yes, my question was aimed at just that, whether there was any other theory that could give an explanation dispensing with dark matter, in case in the long run all attempts to find it failed. I read a bit about MOND theories and, although my knowledge of physics is not enough to understand them more than superficially, they don't seem to have much acceptance in the scientific community. So, as you say in your answer, the best way forward, at least for a few decades, is to keep looking for dark matter.