So here is a question. Borg tech, SG-1 replicators, the cyborg superman. Who absorbs whom? BTW nice Cyberman Borg crossover comic coming.
In the case of Trek, there's no reason to think that the Borg won't assimilate the whole Universe. Until "someone" gets in to their Computer System, and resolves the equation for their obsession for assimilation to say enough is enough, then they will probably continue.