If you have a survey that has already collected responses and then go in to edit the content, whether it's to change a question or edit the answer options, this could potentially wipe out response data. If this happens, the only way to correct it is to undo the changes that were made.
As a general rule if your survey has started collecting responses, do not edit any of the content. Instead, clone your survey and make the changes to the new version. This keeps the reporting separate, and you don't loose any data.