It's not the best reveal, but at least they didn't tack a fake-out on top of it.

There's a Mark Evanier/Sergio Aragonés spoof from a couple years after this issue, that features "I'm quitting the Fantastic Four!" about a dozen times. It's funny 'cause it's true! From 1994, Fantastic Four #392, "The Final Gantlet!" Plot and script by Tom DeFalco, plot and pencils by Paul Ryan, inks by Danny Bulanadi.

Three of the Four are dead here, along with the rest of the planet, in a reality where Reed tried to retrieve the Ultimate Nullifer--instead of Johnny, as in our universe. The Watcher Uatu had subbed in our more experienced Ben, Sue, and Johnny in an attempt to save that world, which failed, and they died. Except the Watcher saves them, to return to their world, although Johnny notices he also seems to imply he knows exactly when they were supposed to die. Uatu does him a favor and doesn't tell him.

Their own Reed was still missing, presumed dead, but Four Freedoms Plaza is crowded; with the Sub-Mariner, Ant-Man, Johnny's Skrull 'wife' Lyja, Franklin Richards aged up to Psi-Lord; and later the Black Panther and what would later be the Fantastic Force. Lyja's false pregnancy, that had tried to kill them all in a previous issue, had been dealt with; and she suggests she and Johnny could think about a real family of their own. He is not especially receptive to the idea, feeling Lyja had played him for a chump while pretending to be Alicia. Stung by that, and possibly tired of the danger, the Torch quits with the traditional fly-off-in-a-huff. Charitably, Sue felt that Lyja had proved herself, and deserved to be there, but she felt she didn't belong there without Johnny. Down to her and Ben (and like eight other people...) Sue thinks the team is at a crossroads, if not the end. Cue super-villain attack!

The Dark Raider appears, demanding the Reed Richards of that world, and recognizing Sue and Ben from their attempt to save the aforementioned alternate reality. He has a ton of tricky weapons, and holds his own against the lot, then unmasks himself when Uatu appears: it's the Reed from that doomed reality, of course. But his theory was, countless earths had been endangered or destroyed by the curiosity of various Reed Richards, so he had been travelling to alternate realities, killing Reeds. He had an Ultimate Nullifier, so there were in a pickle. Working with his mom, Psi-Lord projects the Malice persona that had been trapped in his head, into the Dark Raider's, giving them the chance to grab the Nullifier. Trapped in a force field, bad Reed is impressed, but it's just a minor setback, and Uatu agrees: someone as resourceful as Reed would of course escape eventually. While Sue and Franklin take the high road, Uatu had been afraid of that, and takes matters into his own hands, killing the Dark Raider!

Uatu was afraid the Raider would have eventually won, and says his goodbyes: he will return that Nullifier to where it belonged, then exile himself somewhere with nothing to watch. Uatu doesn't say if their Reed was still alive, but Sue takes it upon herself to find him, saying her own goodbyes and declining help from Ben or T'Challa before leaving on the time sled. (Namor doesn't appear the last few pages here, either to encourage or discourage her.) Only Ben remains, but he resolves to continue, even if it's as the Fantastic One. Which sounds like a pretty good ploy to get Johnny back on board, he'd never stand still for that.