So I'm going to start playing a Deathwatch game soon and I am contemplating playing a Soul Drinker, since they're probably my favorite chapter of all time. Now, if you're not familiar with them and don't care to read the link, then the main problem I run into is that they were declared excommunicate traitoris.

What I want to know is what happens when a battle brother, say one of the Soul Drinkers, is serving in the Deathwatch when his chapter is declared excommunicate? While it might be feasible to become a Blackshield and stay loyal, what happens to the marine that was not connected to the heresy and will not forsake his heraldry?

Well, DW supplement Honour the Chapter has Astral Claws as playable Chapter and we know where they went.

"Couch"Red Corsairs"Couch"

Jericho-Maw Gate was discovered in 755.M41, Achilus Crusade started 777.M41, Badab War happened around 904.M41 (relevant for Astral Claws/Red Corsairs). Couldn't find or remember if there was any dates when Soul Drinkers turned renegade so hard to say.

He might be questioned, Mind Proped to know if he is Corrupted, Executed, Made Blackshield, etc etc

Good question!

I don't think anyone can be forced to become a Black Shield. At least, the write-up in RoB makes it come across as a purely voluntary way to atone for past sins, and barring purity testing nobody is even allowed to ask about the character's history (though some might be suspicious and investigate). So I doubt an established character would suddenly lose their Chapter-badge pauldron and be forced to 'take the black' as it were.

I think purity testing, interrogation by a Chaplain, etc are all totally appropriate.

Execution? No, unless the character is a proven traitor by his words or deeds or spiritual corruption.

Effectively that guy would be seconded to the Deathwatch for life, since there's no chapter to send him back to, and if he's a true loyalist he would be outraged by what happened (and possibly feel guilt about being unable to try and prevent it). He'd probably get a lot of flak from Ultramarines and BTs about it, which would lead to...

Some great roleplay as to why some DW guy post-Badab War is still wearing old Astral Claws heraldry as his missions continue! Especially as he probably would be very invested in destroying the new members of the Red Corsairs who sullied and ruined his chapter.

Or since the deathwatch would control the flow of information to the marine he could end up like Chyron from the deathwatch novel. They could just tell him his chapter has fallen since if you read the end game portion of that thread it says the Imperial Fists decided those who fought against the corrupted were found to be true loyalists.

I would say it depends primarily on why the Chapter was excommunicated.

Geneseed corruption? Doctrinal heresy? Alien influence? Some reasons may warrant a full-scale purge of every single individual, whilst others depend heavily on specific timeframes or individuals within the Chapter that would leave the Marine seconded to Deathwatch innocent/untouched - although that Battle-Brother's loyalty would warrant careful examination in any case, as it may be difficult to foresee an individual Space Marine's reaction to his Chapter being destroyed or, at the very least, driven into exile. It could range from righteous anger at whatever caused the fall (accompanied by renewed purpose and a drive to rid himself of his shameful past by exemplary service) all the way to turning him against the Imperium that has "betrayed" his brethren as well. If he is told the truth, that is ...

Another factor could, of course, be the willingness of his superiors to shield a Brother-in-Arms against perceived injustice, or simply because they value him as a fighter - regardless of whether one would go by FFG's fluff about an independent Deathwatch, or the original material that would see the Deathwatch operate under the auspices of Ordo Xenos Inquisitors.

But yes, as has been suggested above, the end result could be anything from just keeping him in the dark, to a series of grueling tests, evaluations, and interrogations, to a quick execution, to doing nothing.

Here is an online backup of the Index Astartes article that came with White Dwarf #303, dealing a bit with the issue of excommunicated Marines; perhaps it can be of inspiration to someone.

I'm really uncomfortable with just saying to a player "whelp, your character's Chapter did some shady stuff while you're away, and while you haven't done anything specifically wrong, um, the Powers That Be have determined it's time for you to get the Emperor's Peace." And they they take a couple meltas to the face.

On the other hand...if, mid-mission, that character is suddenly attacked by an Imperial Assassin...assuming he survives, that opens a plot to discover what Inquisitor sent them to kill the character, and why. And even if he doesn't survive, his Kill-Team (and possibly even his Watch-Captain) would want some answers and possibly some revenge.

I really hated what the Adeptus Mechanicus and Inquisition did to this chapter. My sympathy was with them all the way.

I seem to recall all of the Soul Drinkers surviving the First Chapter War mutating. Since it is due to their gene-seed, would the hypothetical Deathwatch marine mutate as well? If so, what would be the general response, and how would you represent that in rules? Rolling on the RT/DH tables?

Sarpedon was the first to mutate and following the first chapter civil war, the rest did - from Warp exposure/Tzeentch patronage, not due to an inherent thing in their geneseed.

regardless of whether one would go by FFG's fluff about an independent Deathwatch, or the original material that would see the Deathwatch operate under the auspices of Ordo Xenos Inquisitors.

I like the idea of Deathwatch being independent (only in the most thinnest sense) from Ordo Xenos. Watchcommander chooses how to train and equip Kill-Team. Inquisitors of Ordo Xenos provide the Intelligence where to send said Kill-team, with possible Ordo Xenos agent along. This agent could give commands to Kill-Team if mission parameter would require that.

Sarpedon was the first to mutate and following the first chapter civil war, the rest did - from Warp exposure/Tzeentch patronage, not due to an inherent thing in their geneseed.

Yeah Abraxes was pulling quite a many strings to make this happen. But he wasn't the only laying claim on Soul Drinkers when you think that one Sergeant who devolved into Khornate Berserker.

All in all, Soul Drinkers gene-seed was quite stable not including their hyperactive Omophagea,

On the other hand...if, mid-mission, that character is suddenly attacked by an Imperial Assassin...assuming he survives, that opens a plot to discover what Inquisitor sent them to kill the character, and why. And even if he doesn't survive, his Kill-Team (and possibly even his Watch-Captain) would want some answers and possibly some revenge.

Oh, definitely. Even if he is 'officially' cleared, other inquisitors (or even other Deathwatch battle-brothers) may take it on themselves to intervene personnally.

I just want to have a Dark Angel with the Deathwing advanced speciality in the same kill-team as an Executioner.

"Executioners? Forgive me, I know little of your chapter's history."

"A sad one. We fought in the Badab war, but discovered we had been tricked into siding against the Imperium and betraying the Emperor in deed if not in intent."

"...Eh?"

"We confessed immediately to the Inquisiton, and were sent on a hundred year penitent crusade - after which we were declared fully forgiven in the Emperor's eyes and allowed to return to the Imperial fold. Oh, and the Inquisition is assisting us in hunting down any surviving renegades from our chapter. Which makes things a lot easier."

".......I...but....you can do that?"