A couple of options worth knowing about since I don't know/own the games:

1. A DRM free version looks like it's available at GOG. This is probably the simplest solution to not have to worry about any potential issues
2. People seem to be reporting that the Steam version can be launched directly from the executable bypassing the launcher. If there is a Steamworks DRM check you could always use Goldberg's steam emulator to get around that for fully offline play.