https://launchpad.net/ubuntu/+source/sun-java6/+publishinghi...
Easy to undo if an insecure version is acceptable to you, and once installed, use apt pinning so it doesn't get upgraded anymore.
Honestly: I have never known Ubuntu to keep an old package around. There was a new update released today, 6.26-2natty1, and the now hours old version 6.26-1natty1 is already marked: "removal requested in 16 hours". Do you have a more serious suggestion for how the old packages could be obtained?
https://launchpad.net/ubuntu/maverick/+source/sun-java6/6.24...
No, I was not trolling you to waste your time.
All old packages are archived in launchpad, even after they get removed from the archive.
At this point, you are presented with the "(deleted)" notice next to the file. In fact, along this path you have been presented with "(deleted)" next to every useful download (such as for sources); the only thing you can get is a 318.5 MiB diff from 6.22-0ubuntu1~10.10.
So no: old packages are /not/ archived in launchpad, and I feel you are just helping prove that. Accordingly, I will now reassert my question re wasting time. Seriously: this is ridiculous; are you even trying these links before claiming they work in specific ways?
I mean, this isn't even something they could easily undo: the old packages won't be able to be distributed anymore. They would either have to manually install the SDK themselves in a way compatible with the Ubuntu package distribution, or install OpenJDK and hope for the best (which, as you yourself point out, is unlikely to work, as there is likely a reason they installed the Sun JDK in the first place).