I have seen a number of different posts regarding itinerary changes and associated fees and YQ. The AE T&C details the fees for voluntary changes ($90) but is there an official policy for involuntary changes ie carrier schedule changes?

What happens in cases where flights are pulled from the schedule or flight time changes cause a missed connection or change in departure date?
Does AE contact you to figure out an alternate itinerary or do they just make changes for you?
If they make changes for you but you don't like them can you call and make changes without having to pay the change fee? If so, are you able to make changes to your entire itinerary or just the part affected by the schedule change?
Are you able to make a change onto any Star Alliance flight or only those which show up on AE?
What happens to taxes, fees and YQ for the changed itinerary? Do you get charged the difference if they are higher?

I know these are many questions and any feedback you can provide would be appreciated.

This was triggered by changes to my existing itinerary. I have an NA-Europe1 trip booked. The last portion is IST-BOS-YYZ (I am in IST < 24 hrs and IST-YYZ was not available). On the BOS-YYZ leg (AC #7669) only the last flight of the day works due to the arrival time from IST. I have since noticed that that flight has been pulled from the schedule. I have checked the AC schedule and they are adding another flight (AC #7629) which will work but for whatever reason this is not bookable on either the AC or AE sites. I have not been contacted by AE and I am not able to check my booking online to see if I have been switched to this flight.

I am planning to call AE to find out what is happening. Even if the AC #7629 flight is actually available, would they be able to switch me to a direct IST-YYZ flight without a change fee? If so, are they able to do this if there is no reward availability showing on AE for direct flights?

Thanks