I don't think they would kill off the AIOs at all, because Apple is all about simplicity uber alles. Apple knows there is a massive portion of the general populace that wants a very simple plug and play solution, and that's what the iMac is.
Apple really does seem to be on its way to eliminating towers though, almost as if the tower format were a relic from its past that it wants to purge. There is no reason for an average consumer to buy a Mac Pro. None. An iMac will get the job done just as well, and the only thing a Mac Pro has over an iMac, realistically, is expansion slots, more processor cores, the ability to handle more RAM than 8GB and more HDD slots.
So unless you specifically need more than one internal HDD, more than 8GB of RAM, more than a quad core i7 or an expansion card of some kind, or maybe a 30" monitor there's no reason to get a Mac Pro. Although even the iMac can drive a secondary 30" monitor, come to think of it. So that limits its usefulness to professionals, not consumers, and I strongly believe now that Apple is trying to get out of catering to professionals altogether. It started with the XServe RAID, then the XServe, then OS X Server, and I think the towers are next.
With the advances in technology, it may come to a point where we are able to get literally the same performance out of an AIO as we are from a tower, and there will just be iMacs and Mac Minis. It's doom for the towers! Doom!
*gasp* DOOOOOOOOOOOOOOOOOM
http://www.youtube.com/watch?v=_49iNqxOnH4