Complex sentence: It must, therefore, be concluded that one of those Zombie Sentries must have been from still another parallel-Earth, where a similar outbreak occurred or, at the very least, was narrowly averted.
Split into simpler sentences: It must, therefore, be concluded that one of those Zombie Sentries must have been from still another parallel-Earth, where a similar outbreak occurred! Or, at the very least, was narrowly averted.