Theory of Rogal Dorn's return.

[Karhedron]

The Lion has only had a single novel since his return with the rest being snippets in the DA codex. While Guilliman's return has been hugely impactful in the lore, they have barely begun to address the return of a second Primarch. This is why I don't expect to see another return before 11th edition. I was hopeful we might see Russ towards the end of 10th edition but I am now doubting that. Logan Grimnar has been released on a massive base and is clearly designed as the SW centrepiece model.

[Jamafore]

One way they could run Dorn being gone is what happened to the Chaos ship he supposedly died on? Did the fists have to grab his hand and get out because it was getting drawn back into the warp, has it been seen again? Did it explode rather quickly? For the first, he's been trapped on that ship in the warp and the warp conveniently just spit it back out, or a hulk that it is a part of, recently. For the second he tried to do an emergency teleport before it went boom and has been stuck in the warp for all this time. Both would be contrived, but also make just enough sense, as there are at least precedence for the first, and the second goes through the warp where shenanigans abound.

 

The only way I see Curze coming back is something 40k Theories did a while back. Apparently his crown was stated to have a glowing jewel on it, which could possibly be an Eldar soulstone. The theory being that when he died, his soul went into the stone. And last novel to have the crown, the 1st captain (not Sevetar, but his name escapes me atm) was chasing it through a hive city. So it is possible that the 1st captain may show up being 'possessed' by Curze in a similar manner to the Eldar Phoenix lords

[Karhedron]

The Fists grabbed Dorn's hand and abandoned ship. The Sword of Sacrilege has been active in traitor forces over the millennia. It was eventually dedicated to Tzeentch and took part in the Gothic War alongside Abaddon's fleet. I don't think the existing lore contains a trapdoor for Dorn, but also it does not confirm he was killed. He is just "missing, presumed dead".

 

Basically the only 2 loyalist Primarchs whose locations were confirmed in lore have now returned. The two who were confirmed dead (Ferrus and Sanguinius) are likely to remain so for the forseeable future. Russ, Corax, Khan and Dorn disappeared without being confirmed dead under mysterious circumstances. Vulkan actually returned during the War of the Beast and was apparently killed destroying the Waagh reactor. He is a Perpetual so could still return but it has been confirmed that even Perpetuals can be killed by powerful psychic attacks/weapons so whether he could return from that is unknown.