Nightfall said:
Nah it's not bad. But the Orcus worshippers might take umbrage at Vol's claim to be the one to discover undeath. Orcus proves he can handle it and come back.
I'm not sure that they even claim to have discovered undeath actually, just that they have a much more pragmatic outlook on it ("Yeah, it sucks and is creepy, but it beats oblivion till we figure something else out").
Orcus might have a claim to fame that he was the only one who managed to survive the last days of the Age of Demons. He figured out how to use is unholy powers of Undeath and slip under the radar of the Coatls as Tenebrous instead of just reforming after a while like the other Rajahs. The knowledge of how to exist between discorporation and reformation makes him envied and hated.
It took him a while digging about angelic graveyards in Syrania, interrogating yogoloths in the black gloom of Mabar and discovering just what demiplane hole his Wand was stored in when Khyber was bound in Silver Flame by subverting the elemental lords of Lammania to scour the world for information... but the Bloated Goat might just be walking the face of Eberron right now. Or at least, Tenebrous is flitting hither and yon pulling influence away from his fiendish rivals in effort to bring his wand to the surface, bathe it in the desecrated heart's blood of a coatl and return to power.
Orcus in Eberron would have no fiendish allies, but be the best bet to escape his prison. That opens up all manner of strange bedfellow adventures since even the most ambitious of Rajahs would postpone plans for a generation or two just to keep him from being the first to consolidate power.
Or the holy radiance of the Silver Flame blasted Orcus to the Outer Dark where he grew in power beyond the rings of Siberys and now is in place to hurl Demon Shards down to the world that plant fiendish links to Mabar and spew the energies of Khyber to the surface.
I was going to go further about death aspected areas growing around skull topped crystal towers, but I realized that lunch is getting on and I was just pulling inspiration from Necromongers anyway.
Plane hopping PCs might have to go to Dolurrh to negotiate aid from Marut forces as well as from the demonic eaters of wicked souls (Gabberslug was one, I forget the name) for the forces that Orcus works with pulls souls from the natural order (pissing off maruts) and starving the ... whatever those demons are. They might remember and hate Orcus themselves and have knowlege of his wand and how it might be used to shatter his remaining power.