Today in the middle of the afternoon it logged out and I had to log back in again when trying to sync some typefaces from Adobe Fonts.
The joys of a an always connected workstation. At this point, subscription based software might as well be a PWA (of course, you'll have to run something other then Firefox for that, really bad decision on their part, but I digress). With things like WASM (natively compiled code that targets the browser versus a specific OS and Arch), we already have AutoCAD in the browser, may as well have others (I already have Ps-like and Ai-like programs that run in the browser as it is), shoot, can even emulate other OSs in the browser, that's how powerful that (essentially) "run time" is. At least with browser based programs, it can be run on any OS. Just have to be careful, the client can't be too "thin" on resources as the browser is able to take advantage (and needs to) of hardware on the client.
Given how features have been removed with little notice and typically due to Adobe and it's issues with licensing with these 3rd parties, anything that I would use that is a 3rd party licensed blob of code that isn't totally controlled by Adobe, I would make sure that I have a way of "finalizing" what ever it does, just in case they (Adobe) pulls the plug those files aren't essentially useless (while you mention fonts in this particular section, I mean anything, not just fonts (sometimes can find this in the "About "Program" section, it will lists copyrights, for instance an Eastman Kodak toolkit is in Ai CS6).
I'm pretty sure the registration and activation servers for CS4, CS5, CS5.5 and CS6 are still operational. But there is no telling how long that will continue.
I'm pretty sure that they are as well, but that's why I said "
if they shut down...". Commercial grade servers tend to have a 10 yr warranty, so anything (and it may not even be true if they even say it, could just be an excuse) could happen, likely hood of normal wear and tear just went significantly up on that hardware.
I imagine Adobe will follow a similar approach when they gradually take down the servers for the rest of the Creative Suite versions. Don't throw out those old boxes of software!
If you are talking about the serial numbers, I would just make copies of that somewhere else, that way even if one doesn't throw out the old boxes, at least there is a back up that.
Now, if you are talking about a backup of the old discs, I would actually suggest creating ISOs of those discs (and store the activation number with them (or within the ISO itself)) that way you have a backup and as optical drivers are getting less and less prevalent, still have the ability to install as most modern OSs recognizes ISOs as virtual drivers and they will appear to the user as such. The one caveat here is don't use archiving software to do this, the chances are high that they will truncate file names without any warning to the user and that will render the ISO useless for installation. Use disc burning software and when warnings appear cancel the request to truncate file names. It used to relate the Joliet naming schema, but those requirements are outdated.
Another thing users will have to keep if using old versions of Adobe software: their older installers for plugins. Some of the newest plugins are not backward compatible with old versions of Adobe software. The latest versions of Astute Graphics' amazing suite of Illustrator plugins require the CC version of Illustrator.
Astute graphics makes great plugins, but I don't like how they handled things with regard to their licensing. It's misleading at best. They say, that you can keep the plugins that you already bought when they went to the subscription service to keep getting the latest and greatest, but with Adobe's aggressive mandated upgrade schedule of customers always needing to be at least on x-1 version, the user will needs to stay on that subscription service for Astute as well. As any Adobe update at any point in time could render the version of the plugins that you have useless. Bare in mind, this policy of Astute came out
AFTER Adobe changed their policy due to what happened with Dolby. So they don't even have the fact that they had this policy before the change in Adobe's upgrade policy in their favor.
I really enjoy their plugins, I have them for CS6 and they are great (finally have the wacom airbrush pen support in Ai due to the plugin), but that policy really needs to be changed and just need to be perpetually on the subscription service now. I don't like it, but I wouldn't blame them for that as much, because it's really Adobe's policy that makes it necessary.