I get the impression that WOTC would really like it if D&D 3.5 would die a quiet death and do so soon. Unfortunately, I don't think that will ever happen as there is now no realistic way to prevent the nearly no cost duplication of all the major D&D 3.5 books. I say someone bragging online about how they had the major WOTC D&D 3.5 books (about 60 of them) and 15 WOTC Forgotten Realms books in PDF format on his computer, taking up just over 4.2 gigs of space on his hard drive.
I have no idea how much these cost him, but probably a lot given that PDF copies of books are not discounted nearly as much as they should be. But at about 4.2 gigs of space, they will all fit on a single DVD. I recently purchased a package of 50 DVD-Rs for $16.99 which works out to about 34 cents a DVD. That (and 10-20 minutes of copying time) is how much it would cost him to give a copy of these 75 books to a new player. That new player would be able to do the same for another new player, etc.
Is this legal? Of course not, but neither is copying music CDs for your friends or the like and people have been doing that for years (as they did with tapes and records before CDs). With the cost of entry for new 3.5 players being effectively nil and WOTC having no way to kill the supply of copies, I expect D&D 3.5 will have many players -- and many new players -- for years to come.
It's always been hard to kill off older editions of D&D as some players just prefer them and were willing to track down used copies for new players to keep their campaigns alive an growing. Between easy to copy PDF editions of the rules and the OGL allowing new 3.5 material to be published forever, I suspect that D&D 3.5 will have a very long life indeed.