Is it too late to use a CDN? [closed]

I’ve got several blogs and a couple of them are pretty visited, with around 1,5 million uniques per month. I’ve never used a CDN on them, but I’m considering trying to set up an account on some of the platforms available that have good support in WordPress through plugins and a nice user community.

I wonder though if this is a good moment to do this, because until now all the images are hosted on the server, and I guess after setting up the CDN all the images should be loaded on the CDN servers through the adequate plugin.

I guess that from that moment on, all the articles and posts we publish would benefit from the images loaded through the CDN, but the past articles would not benefit from that. I wonder if:

1. Is there some easy way to use the CDN for the old posts too?
2. What happens if I decide I want to run my blog again from my own server
   (for any reason)? Would I have to re-publish everything with the
   images I already had in the CDN servers? Is there an easy way to
   recover all the images and make them load “locally”?

The main problem for me is knowing that if something goes wrong I can have avoid big problems if a I switch off the CDN and decide to run everything back from my servers. What happens with al the content I was serving from the CDN? I hope you understand the question.

Most CDNs (including Amazon’s Cloudfront, which is what I’ve used), allow origin pull, which essentially means that the CDN pulls the required entity from, in this case, your blog, the first time someone tries to access it.

If use a caching plugin like wp-supercache, or w3 total cache, they integrate with CDNs like Cloudfront to manage much of this for you. So, I can turn off my CDN by unchecking a single checkbox. This then reverts all image, js and css references back to the original location – ie your server.