One of the goals of Teletype.net is to archive as much teleprinter-related information as possible for preservation. To this end, we've established a special crawler that parses known teletype-related sites (with the owners' permission, of course) and backs them up redundantly. In the event that the site becomes permanently unavailable, we will upload the latest snapshot of it here.
Yes, the Internet Archive most likely has also archived much of these sites away, though it is known for missing pages. This way we ensure we archive everything we possibly can. It is impossible to save precious data too redundantly.
If you know of a teletype-related site that is not on the below list, or if you find that one of these sites is no longer functional, please contact me.
List of Mirrored Sites