To me the worst case scenario (not much discussed in medias for obvious reasons, but I think clearly foreseen by some experts) was (and maybe still can be) a level of contamination outside of the containments which would force humans to retreat from the site, then of course we can imagine the worse domino effect with situation degradation on site and radiation worsening, disabling any possibility for operations with humans without complete sacrifice.
Even if the containments are breached, most of the fuel is still right now under water (SFP) and shielded by big amounts of concrete in the reactor buildings. If a fair amount of fuel is exposed outside on the ground (SFP explosion or fall, core explosion, etc.) then no more shielding and the worst case scenario above would probably happen. This would be even worse if some re-criticalities could happen (big discussions on the forum to know if it can happen, and even if it locally happened, by the way).
With the amount of fuel in the plant (reactors + spent fuel), and a situation completely out of human control if no human presence possible, one could imagine that the location could become so dangerous than maybe even the Daini site (12 kms away) could be difficult for humans to stay. Then who knows what could happen...
This is a real worst case scenario, with worst domino effect, to answer your question. We were not so far from this with the Attic SFP, big luck that none complety exploded exposing the fuel on the ground.