Look. Valve is not going to have a temper tantrum and throw away years of work because somebody stole its favorite toy without asking. Sure, it sucks. But overall it's really not going to change anything. There will be a few extra hacks (like there weren't going to be ten thousand anyway), there will be a lot of grief and flailing of limbs, and life will continue essentially unchanged. No corporate project is going to use the source and no free project is going to use the source - they'd get sued into oblivion. Yeah, a few people *might* look at it and come up with some "ooh, that's a neat idea" tricks and put it into their own source. It happens. It won't make more than an incremental difference to their game - if it was gonna be good otherwise, it'll still be good, and if it wasn't, it won't.
So get over it. Life goes on. Valve didn't just suffer a multi-million-dollar catastrophe - they suffered maybe a fifty-thousand-dollar catastrophe, and with all the PR they've been getting over this, I'd be willing to bet they actually made a *profit* off this.