It's possible, and probably likely. Killing a dragon doesn't look as involved as going into an Oblivion Gate to close it, so I could totally see them being left in (at a reduced spawn rate) so that players have something "big" to do every now and then. I wonder if Pete Hines would answer that.. let's find out!
EDIT: Okay, I Tweeted the question to him.. hopefully it's something he is allowed to give information about.
EDIT2: Probably not going to get an answer from him this time. Usually he gets back to you right away if he's on Twitter.. if not, it'll probably get lost in the shuffle with all of the other Tweets he receives. Someone should try again in a few hours.. but let's be easy on the guy, apparently he's come down with a sinus infection. =\