I'm just playing devil's advocate here, but we could also just be doing some basic fishing for some McGuffin in another zone. We clearly need a Maw Sigil to follow Zovaal. If they wanted to they could just make a raid in some proto maw zone that floats somewhere in the middle of nowhere that was something like Zovaal's original realm. There we uncover something about him (with out actually meeting him at all in 9.2) and reforge his sigil after dealing with a few pests there that have taken overt the place, like some devourers, brokers, first ones creations and maybe some original Zovaal flavor enemies. We know practically nothing about his original character.
That would practically be Blizzard's last chance to cram in some much needed exposition for him and flesh him out before we take him down. Time gating that over 8 weeks otherwise after you've already butchered him in normal/heroic in the first week of the final patch is certainly not going to do it.
While I doubt it personally from a business PoV, it could be a possible from the way video game stories usually work. I certainly hope they won't have him vanish off into the distance a 2nd time. Turning this into a "Your princessgimp is in another castle" meme isn't bound to resonate too well with people, though I doubt neither is going on what amounts to a side adventure after we already did so this patch with the whole sigil gimmik (introduced and immediately resolved).