I had a repeating RSVP event defined and when I updated the Note To Send Attendees text and saved the change for all in the series it deleted all the responder details for each occurrence! A separate test has shown it does this if you update the event description too. I'm not sure what happened as the first event in the series was also removed from the calendar but there's no Activity Log entry to say it had been deleted. Updating the text for a single occurrence RSVP event does not delete the responder information.
I'm sorry about this. I'm trying to duplicate this but I can't. I create a repeating event, with rsvp. Then I rsvp to one of the events. Then I change the Note To Send Attendees text and update all events. That works for me. Am I missing a step?
As for recreating rsvp details, I don't have any suggestions off hand. I will keep thinking about it.