There is a market for this lens - people like me. When the autofocus failed this summer on my Sigma 100-300 f4 and two repair places and Sigma all said it is too old to fix, I had to go for the Canon 70-200 2.8 as replacement. No way I could afford the IS version, so I got this one (which I really could not afford either, but I need it). I need the 2.8 for the shallower depth of field (often I combine with 1.4 extender which puts me back at f4). After my experience with Sigma, I would not feel comfortable replacing it with an aftermarket lens. But if this lens were not available, that would be my only choice. So Canon will lose a few sales to people like me, but I guess there are not enough of us to worry about.
As for used lens prices going down, I think not. Even the old original (black) 80-200 2.8 sells for 800 bucks, and that has the slow AFD autofocus and does not take extenders. These lenses hold their value and the discontinuation of the new option will make used versions even more sought after.