That's true. If Canon releases a 5D3 with the same AF as the 5D2 or even 60D I would probably just buy a cheaper 5D2. I'm certainly not on the fence for switching. Canon would not lose my business they would just lack a sell of one 5D3. I think they can deal with that.
That's the other problem for Canon from a marketing point of view; if they don't do something more than simply change the sensor for the new 18MP one, there will be a lot of people in this position. The last thing that Canon wants is 5D MkII owners not bothering to upgrade and potential full frame upgraders settling for previous 5D models. If they do use the 18MP sensor, I cannot see the point of a camera that has great high ISO capabilities without the AF system to allow you to fully utilise this. After all, the whole point of using high ISOs is to enable you to raise shutter speeds in low light!