A Male to Male standoff could be awesome. I dig it!
It could come at any time (well maybe only starting after the player has the two lionesses on field or something). The only thing you can do to influence this is make sure the pride belly is full to increase his chances but (assuming as is Lion Cod of Law, no clue here, I assume not get involved directly in the fight itself). The challenging lions will start off weak but will tend to be stronger over time (at least as I'd see all of this implemented in Survival or a spin-off version of Survival). If our original lion loses the game ends.