s3 offload and media managment

I'm curious about some of the details of how the s3 integration works.

If I have media files offloaded to S3 and removed from my server, what happens if I need to regenerate thumbnails, crop / edit an image, duplicate an image etc?


Do you replace any media links that are already in our content, and if so, what is your method? (Database editing or Replacing URLs via php/scripts)

Do you have a method that would allow a shared cloud library (s3 or otherwise) across an entire multisite network? Site Authors could view shared media, and choose to use individual images without having to have the entire library synced to each site.

Thanks for your help!

-Dan