Well, if Kirk did get assimilated than most likely the plot would've gone the same only with Spock mind-melding with Kirk instead of Data interfacing with Locutus.
Kirk's faced super-technological beings before, like V'Ger. Without Spock in that story I'm not sure how things would've turned out.While Scotty deals with having acting command (Spock having been bypassed because his technical prowess as Science Officer is logically needed more urgently in this situation) and trying to quickly come into his own with some original strategies that Kirk won't be familiar with...
Scotty would fill the Borg cube full of Tribbles and cases of Scotch. Let's see how those cybernetic beasties deal with that.