It's speculation from a set of people that love to give doomsday scenario's.
"if" is the key word. What "if" nobody picks up and maintains a abandoned piece of code? Same thing. This isn't the Minority Report where you are guilty before you even commit a crime but that's sure what the foss'rs like to make it sound like. Nvidia could just as easily say "OK we give up maintaining them, here is the code".But if one day nvidia decides there's no money in linux desktop drivers then there's no free alternative and we're all screwed (I've got a nvidia card too).
Again HUGE "ifs", let's at least have a dead body before screaming murder.See Oracle's recent takeover of Sun for example - what's going to happen to OpenOffice or MySQL? Maybe they'll keep supporting them, maybe not. But it doesn't matter so much because they're open source and therefore forkable if someone wants to maintain them.