I would imagine the MP count of the next 5D to be higher of that currently available for the 5DII
But I don't see the 5DII going anywhere either. AF aside its got a huge place in the industry still with little coming close to it.
Apart from Canon 1DsMkIII, 1Dx (5DMKII) and Nikon D700, D800,D3/s, D3x, D4, Sony A900, A850 etc., etc. Which all offer FF performance sensors AND additionally provide pro AF/metering/body and the newer Nikon and Canons offering superior video performance (in particular the Nikon D800 and D4 allow raw uncompressed output over HDMI).
The 5DMKII is only unique in that it puts a high-end sensor in a low-end body, while everyone else puts a high-end sensor in a high-end body. This worked fine for Canon last time round. For studio/landscape/macro/ the 5DMKII may have a place but these areas will as well if not better be served by the alternatives and new cameras.
That doesn't mean the 5DMKII might not continue to be sold. Who knows what is in the stockpile or what Canon's plans are.