[@Wraithblade6] Just to clarify, how many stories did Xepherial fall? Because it seems like it was a lot, like a lot-lot, since as a superhuman in power armour he managed to both knock himself unconscious and have a background spike pierce his power armour. Now, power armoured superhumans might be able to survive that, but without power armour, they probably wouldn't. Lucius knows this, and I'd assume that leaping into a who-knows-how-deep pit is a good way to commit suicide, even if you have superhuman strength.

Besides that, Ga'duk already went a different way from the pit. Unless I want to split Lucius off from Ga'duk, which I'd rather not considering they were already planned to join forces, I can't have Lucius follow Xepherial into the pit, and the doorway is sealed off by a sheet of plasteel and a horde of Genestealers, so I physically can't make Lucius drag Ga'duk back to that point either in a particularly timely fashion.

And finally, there's really nothing Lucius would add to Xepherial's arsenal to help protect him from Traitor Marines. He lacks power armour, and his only weapons are a sword and a knife - both Space Marine sized, true, but compared to a Techmarine in full power armour, it's not much of a match against any kitted-out CSM. Basically, just be patient about Lucius and Xepherial meeting up, and if you need other PCs to interact with, have him meet up with... Zuriel and Urgrugg, I think is the option here. Either way, Lucius and Xepherial isn't a thing that can logically happen at the present time.