Hi
AliceBissolino,
first of all, congratulations on your invitation to interview with INSEAD.
Unfortunately, the situation you described is not uncommon. Keep in mind that alumni interviewers are volunteers and they interview candidates as a way to give back to the school. So, if they are busy with work and all, the interview could not be among their highest priorities.
If I were you, I would email him once more with a friendly reminder. In this email, be very appreciative of his time. I talk from experience when I say that these interviews take a lot of their personal time. It's not just the interview, but the report they must send after takes time to write. So, it is always good to acknowledge this and be appreciative in your communications with them.
I would also email your AO and let her know about the situation. Worst-case scenario, she will find another interviewer.
And don't worry about the deadline. Deadlines can be extended and the day of the interview has no impact on the final outcome.
I hope this helps.
Warm regards
Alex