Ask HN: Questions to ask departing CTO?

The CTO of the small startup I work for as a software engineer is moving on to another position soon.

I'm thinking of booking a meeting or two with him to pick his brain before he leaves. I want to find out as much as I can about relevant knowledge, thoughts, and opinions of his that might not have come up in our day-to-day work. (Relevant: I've only worked at this company a few months so far.)

What questions should I ask him?