Not all Steam games include DRM. Even if Valve turns malicious and tries to activly delete your local copy of the games. As long as you have a backup of the Steam directory, you would still have access to the non DRM games you had downloaded.
If by DRM you mean the game won't boot up without an internet connection check, then no, most games do not require the internet to run. Even GTAV loads up fine in offline mode. As it should.
Even Ubisoft's Uplay and Origin clients have offline modes.
Games which require the internet to load up, even though they have single player modes, deserve a thumbs down. Steam has an offline mode, and game publishers should respect that.
