Is it possible to write PhD thesis (or PhD level article) in Computer Science without (real) advisor?
Let's not lose sight of the fact that doing a PhD is a very hard thing to do, even with an adviser (and particularly in computer science, but also in essentially any other discipline). So what you're asking is basically "is it possible to do this thing that is difficult enough that a good proportion of the people who try to do it don't finish, but in a way that makes it even more difficult than it already is?" 

To use an exaggerated metaphor, it is a bit like asking whether it's possible to climb mount Everest blindfolded. The literal answer is, yes, it's possible. The practical answer is: any specific person who tries it will almost certainly fail.