I do not think that because he was a dictator he would not care at all.
Probably, he did not want to destroy Mosul and all its people. And even if this did not worry him, taking into account that he was doing this for publicity (either internal or international), he would not have wanted the dam to fail and kill thousands of people.
Yes, if he wanted to kill all the people of Mosul, I'm sure there would have been a lot things that could have been done for much cheaper than building a dam, and maintaining it for 30 years.
Probably, he did not want to destroy Mosul and all its people. And even if this did not worry him, taking into account that he was doing this for publicity (either internal or international), he would not have wanted the dam to fail and kill thousands of people.