I would say a lot of territorial fighting could occur. But this would include a lot of head bobbing and threat displays. As well as chasing each others in circles flattening up. The bigger tougher male would win the fight and the submissive one would loose the territory and or females. I would say death would be pretty rare.

The reason they can kill each other in captivity is because they are stuck in a couple square foot enclosures versus square miles to escape each other. When stuck together the agression can be non stop. There is no break and eventually the non dominant male becomes too stressed to eat. Eventually they wither away and die.

It is best to not keep adult males together unless you have a greenhouse type set up with ALOT of room.