To restore compressed images on WordPress, your images needs to be in the backup time (1 month) then you can use the top selector to apply the image revert (see attached). The all your images will be reverted to the original quality.
Yes that's currently the case. We've planned to add an option in the future to store a copy on your server. That will be an option as the problem is that it can takes a lot of space (while image compression has an opposite goal).