on important threads, like ones that are getting search engine traffic in the top 100, i often go to the wayback machine and try to find the image and host it locally, or replace the image with something else that fits the context.
going forward, use the image proxy, cache images, and set the expiration to never expire so you store a local copy.
or, there's addons to do this to convert everything to attachments, but again, if it's already done, it's too late-- only go-forward images will be fixed forever.
of course, you need the storage space to host it. throw it on s3...
