I think the answer to #1 is basically yes Master and Backup will eventually sync, whether that is milliseconds or seconds, I think it would depend upon what Master RE is doing at that time. At the same time, why even consider this situation. Just add the extra 1 line in the configuration and follow best practice recommendation. if you ever encounter an issue in this area without commit sync set, I assume the answer would be set commit sync and see what then happens.
As for #2, yes only on the Master.