re: Are you supposed to call professors "professor" even after

If he was a former professor and you aren't sure if he has a doctorate or not, I would absolutely call him professor. It's a sign of respect.

If you know he has the doctorate, call him doctor hands down. While using the term professor wouldn't be a crime, it is true that not all professors are doctors so the ones that have achieved that status should be addressed accordingly.

The one I have trouble with is how to address deans. While I feel like a professor w/ a doctorate would prefer to be addressed as Dr. So-And-So, I feel like a dean with a doctorate would prefer to be addressed as Dean So-And-So as opposed to using the Dr. prefix. It seems to me that attaining the status of dean is even more respectable than having a doctoral degree and they should thus be address accordingly.