I have, every time the revised TOS pops up, hit "decline". If I try to start one of the games I actually have currently installed I get the pop up. Hit "decline" and it closes down. The games are not launchable. I haven't tried to reinstall anything I have purchased from them, but just downloading and installing a game I purchased will, I assume, not even be possible without agreeing to the new TOS. Of course, even if I could install one, I would not be able to play it anyway.
I've been going back and forth with Steam Support on this and not getting any definitive explanations to my questions. The only thing I am told is that unless I agree I cannot access any Steam services. Sure makes me feel robbed to not be able to access the games I paid them for already. Not like I use them to play online or intend to ever again make a purchase from them, so they can cut me off from using any of their services aside from being able to access the games I paid them for.
I have also sent some emails from Valve's contact page. Gabe Newell is on vacation until the 24th of this month. I wrote an email to one of the points of contact he recommended in his vacation auto-reply. Haven't heard anything back yet, but it hasn't even been 24 hours at this point.