I really don't think it would be that difficult to kill Hearst, of course not openly in "Wild West style", but if he was shot by covertly like Elsworth or even killed by someone like Trixi, I don't think there would be full scale invasion by outsiders like you said... He would be just another rich man who was killed in lawless town. Also Bullock and All were not dealing the enemy more subtly, they were not dealing with him at all. That was a problem with 3rd season - a lot of talk about what to o with Hearst and then - rolling over and doing nothing.
Well, some people complain about it, but does it really matter? I didn't even realize they were played by the same actor so he pulled it very well.
Really? Those guys were the worst part of show IMO, I always fastforward every scene they are in, all of them were incredibly boring.