Every time Canon releases a major new camera, this discussion surfaces.
Never happened in the past. Not going to happen in the future.
As Mt. Spokane said, Canon has already switched production lines to the 6D2. They can't or won't switch back for a previous model.
The 6DII isn't available yet, but it is already the top selling full frame DSLR on Amazon, so no reason to think Canon needs to offer a lower cost 6D.
As Sporgon says, the 6DII will eventually settle in for a lower price, so patience can be a virtue. But from Canon's standpoint, there is nothing to be gained by keeping the 6D alive.
Consumers want the latest and greatest. Not sure a 6D that has been replaced by the 6DII would have much appeal for most consumers.
I don't know how Canon handles unsold stock with its retailers, but I suspect that many of those unsold bodies will end up back at the Canon refurbished store, where they will be sold at a discount until the stock is depleted.
In short, while continuing the original 6D might be appealing for a handful of customers, it makes no sense from Canon's standpoint.