User said my answer had helped him, and then deleted the question instead of accepting an answer. Can this question be undeleted?
Yes, the questions can be undeleted by users with access to 10k-tools.
However, I don't think that the question is beneficial to any future users. As per a quite famous (and much recent) campaign of removing all typo questions from Stack Overflow, I'll quote from random's reply:
A typo is not the same as a logic problem and seeing results turn up for the former when yours is clearly of the latter is indeed a cycle of bother.