Ellison would still have been constrained to hit the reset button, though, for a tv show in the 60s, and his best stories generally don't end too well, for at least some people.
But I'll give it a go. In "A Taste of Armageddon," the Eminiarans and Vendicarans would have utterly annihilated themselves in short order, proving that their solution of unending war by computer and disintegration chamber really was the best solution for them, and that Kirk was a short-sighted meddler.
In "This Side of Paradise," there would have been mass suicides on Omicron Ceti 3 after the spores had been counteracted.
Devil in the Dark--The Horta and her children would tunnel, but momma Horta would have demanded pay, and probably OT. The Horta is smart; she'd have understood that she'd need wealth to begin to, perhaps, hire lobbyists to work on members of the Federation Council, possibly to get some Horta among colonists to other worlds.
And as soon as she demanded fair pay, the pergium miners would have all gotten Mark 2 phasers and killed them all.