I still don't quite understand how often this happens for you or in which dialogues it occurs.
If Auto mode is disabled, then, as I mentioned before, there are a few rare cases where dialogue lines change very quickly on purpose as part of the scene. If you don't have enough time to read them and really want to, then yes, using the rollback feature is the only way to go back and read them.
However, if this is happening frequently, I'd like to know more details about where and when it occurs.
As for the available content, if there are no quests left in your quest log, then yes, you've completed all of the current content.