Cormier is fucked if he beats Mir. Everyone that has beaten Mir, went on to lose their next fight. It's called the Frank Mir curse, and it's no joke.
The only exception was Lesnar. When Lesnar fought Carwin, they were both coming off wins over Mir. So, one of them would end up breaking the Mir curse. As fate would have it, Lesnar got the living shit beat out of him in the 1st round and won by miracle submission in the second. So, you could say that both lost.
The latest victim of the Mir curse is JDS. After fucking Mir up, he got demolished by Brown Pride Velaques. Cormier is next...