I researched this myself a week or so ago, and you will find MANY threads on the Valve forums (with NO official responses) about this topic. In other words, the “last patch to remove DRM” is an unfounded rumor that nobody can find proof for. Evidently, there was a vague mention in a sidebar of some magazine by Gabe Newell (that’s the best I’ve found as far as “fact”) but no one can seem to remember the magazine, issue #, etc.
Wish Valve would have an official standpoint on this. I think I’ll just install Steam on my home server and download every game I own to it so I can do a backup.