All the images have now been updated and reside on stack's imgur.
If the links are broken
The same as we do with any broken link:
Replace where possible. When replacing upload via the sites tool so it goes to stacks imgur and should not die.
- Maybe you remember the image, get it again. It could also be obvious from the text what the image could be.
- Check the web archive for the relevant pages: Flickr and SFF in case they have the image.
If the image can’t be recovered you can always leave the link and add a note that the image can’t be found after the link died.
If the image is really necessary and can’t be found then it might be more appropriate to remove it all together but this is on a case by case basis.
If the links aren't broken
It would be best to upload these to stack's imgur through the editor rather than to rely on third party hosting. When editing to do this make note to be wary of the 5 in 15 edit policy and try not to flood the homepage too much.