I found some info about abandoned questions. But I saw an answer that did not fit to the question. It has been voted up and down several times. Someone asked the user to delete the answer as it is not correct. But he did not, because he clearly left the site some days after he wrote his answer.
Maybe I could just flag this answer but it is not so easy because the answer can be helpful as others stated.
Maybe an edit would be the proper way. But I feel that edits shouldn't contain something that wasn't in the original version. (At least I cannot say "ok this is not the real answer" in an edit.)