His last body, abandoned with the torn memories of the ancient Archmagos, was rendered Damnatio ad Gladium by the last commands of the intact Xander, and led the majority of the fleets Cybernetica and their newer Genetus monstrosities against the Dark Mechanicum in an enraged vengeance crusade for the destroyed knowledge of Mars, finally being killed (some of his fellow Archmagi preferred to say "put down", there was hardly anything separating him from his creatures by the end) storming Cyclotrathe by Knights of House Atrax.
The fleet is still there, dug into a system that would be a fortress by cosmological standards, even before it became a collection of Forge Worlds, gun platforms and energy farms. The Genetors continued their experimentation, slowly developing research paths that were sealed in the Vaults of Moravec for good reason before, combined with some of the Vodian research from their last homeworld, and before too many centuries had passed could be considered the equal of any in the Dark Mechanicum. Strange corrosive bio-weapons, living ships, creatures of the Warp bound screaming to flesh as the Soul Forge did to metal. Occasionally, a rumour would spread of the "Old Mechanicus" beyond the Ghoul Stars, but aside from a few missing ships little was found besides worlds picked clean and poisoned more subtly than the Plaguefather tended to. Inquisitorial attention had been planned, but was dramatically disrupted by the launching of the Thirteenth Black Crusade.
Working on a custom model for the good Archmagos, will probably nab all the bits in a month or so along with the rest of the stuff I want to finish off my 40k Mech army. Then onto actually getting him a 30k Honour Guard.