Actually, he has the legal system to support his claim. Your entire position is based on the assumption that Valve CAN remove the DRM if they need to shut off their servers. This is incorrect. Many of the games on Steam are not owned by Valve, thus they would not have the legal power to remove DRM from third-party games without the publishers' consent (the very same publishers that fought tooth and nail to use DRM to begin with). Of course, this is assuming they can afford to remove the DRM before something like going bankrupt, to begin with (and good luck downloading games after their servers go down).
So yes, from the objective facts we have available, probability is strongly on the side of Valve NOT being able to meet your hopes. But this is a free country (assuming you live in the US); you're free to put your faith anywhere you like.