Old.reddit.com Isn't Working
old.reddit.com
old.reddit.com
The typical easy way is to have many "unfortunate mistaken outages". This is how Google via Maps and Mail handled Opera 6+ times (iirc), how Facebook handled Opera Mini 8+ times with the login javascript doing more and more esoteric things, etc etc.
I believe Firefox has witnessed something similar in the past few years couple of years with popular properties.
I wouldn't put it past the Reddit team to try to do something similar to push away people from their old, less monetizable interface.
An actual decommissioning would be coupled with a redirect or a note or something.
I don't think they have any experiments where they give a new user the old interface to do a proper A/B test, so I don't think you can conclusively say that people like the new interface better than the old, or vice versa.
Teddit (https://teddit.net/) is a reasonable alternative to old.reddit.com provided you don't care about being logged in. I'm not affiliated with them, but I have used their Reddit front-end quite a bit and like the style.
I didn't see anyone claiming that all of reddit was down.