The old comments aren’t completely lost. If jacquesm wanted to, he could export the comments to XML (http://help.disqus.com/customer/portal/articles/472149-comme...) and then write a custom script to re-import them into a new commenting system of his choice. But unless he does that, then yes, the old comments are basically lost.
I think this should be highlighted: disqus is, at least, until now, quite upfront about telling you that the data is yours and you can take it away, if you don't want to use them anymore.
