The UFC co-promoted with Pride, why can't Dana extend 1 fight co-promoting with M-1?
Brock vs Emelianenko will draw the largest Pay Per View buys in MMA history. So even if the profits are split 50-50, both parties will still be the winner. 50% of Fedor vs Lesnar may be the 100% profit made from UFC 100 or more. You can sell this pay per view to almost any country that knows MMA. This include huge profits from Japan, Korea, Russia and other European countries where Fedor is well known.
If M-1 can show Dana the $$$$ why they should co-promote, Dana will agree. He does not mind Brock losing to Fedor, he knows that already.
Actually the only way Dana would OK a one time fight would be if he was sure Brock would beat Fedor, and Dana's too smart to count on that.
Having a one fight contract in which Fedor beats the UFC champ would not be beneficial to the UFC. It would completely delegitimize the UFC's HW division. That's why Dana wants a multi fight contract and in every other case forces champions to remain under contract until they lose. He doesn't want a reigning champion jumping ship to another organization.