Just my two cents: Canon refurbished lists the 5DII at $1,759 (when in stock). That's with a 90-Day Canon warranty and the knowledge that the camera has been serviced by Canon. When Canon offers its 15% sales, that knocks the price down below $1,500.
As a buyer, I wouldn't look at a used "as-is" 5DII from a private seller unless it was significantly less than that.
As far as how long the 5DII might be available...well...Canon is still listing the 50D on its refurbished site. Supplies are unpredictable, but they still list them and sell them when they have them. Given the number of 5DIIs out there, I suspect they will remain available for quite some time even after they are officially discontinued.