As heretical as it seems, I'm not familiar enough with the grey knights to do them justice. Not entirely sure what their standard operating procedure would be in that setting. You've got a ship from a chapter that as far as most people are concerned, have been isolated fighting off the tyranids suddenly show up and get ripped in half. It's one of those things where i know there are a lot of people who love the grey knights, and a lot of people who despise them. I think Arch Warhammer put it best in his video on them. when they're handled by a good author, what they do makes sense. when they aren't... they do stuff just simply because well, of course they do and it gets rather ludicrous. and this is coming from a guy who in table top for 40k, fields a 3k army of nothing but gretchin.
Honestly? The Grey Knights wouldn't care who the chapter is that the ship belonged to (other than maybe
if it was an original founding legion or a chapter that was under scrutiny by the =][=). They wouldn't care that they were last seen fighting the tyranids either, other than the possibility of tyranid bio-contamination to the ship. They would only care about the fact that the ship was exposed to the warp, without protection, and that anything/everything on board had a possibility of being tainted.
I don't know what a purge team would be there for. well i do and i don't. name is fairly self explanatory. they are there to purge. But what about survivors? What about the original mission of those marines? what about the planet that got smacked by the corpse of a ship... well half of a corpse of a ship.
The ship that we are talking about was torn in half right?
The part I am talking about was cast into the warp and then spat back out was exposed to the tides without a gellar field's protection. Which means pretty much all normal humans on that section of the ship are already tainted beyond recovery, that is if they are not dead already from the neverborne (deamons) that would have spilled into the torn ship and run amok. The Grey Knights would be looking for those 'survivors' to ensure that they were contained. The =][= doesn't just let people who are tainted, or even those possibly
exposed to taint, survive if they are aware of the fact. The Lantern astartes would have a slightly better chance to resist the tainted tides depending on their willpower, however they would have to be thoroughly soul-scour searched (and possibly mind scrubbed) by a Grey Knight librarian for any signs of taint before they would be allowed to leave. If any taint at all was found they would be destroyed by order of the Ordo Malleus.
What you have described of the ship being torn apart and cast into the warp only to be spat back out again is exactly what the Grey Knights would be suited for.
With the recherche i have done on grey knights. Yes i get it, they're stupid powerful. Powerful to a point where overkill is looking up in envy. but the whole mind wipe thing, blank slate no personality or memories... least from what i've read anyway... seems a bit counter productive in an RP setting. I'm not opposed to it. I'm just saying i know i can't do the grey knights justice... I'd feel more comfortable if maybe the grey knights were working with a local chapter. like a local chapter of space marines and the grey knights had responded to the scene at the same time. Who the local chapter is, well that's for you guys to decide.
The Grey Knights are
highly trained, highly equipped astartes under the direct control of the Ordo Malleus so they are lead by an Inquisitor (maybe not physically on every mission, but there would be an Inquisitor with them on their ship). But, they are not perfect (other than their purity) and each warrior has the possibility of making mistakes just like a normal astartes to some extent. They are also bound to the order of the Inquisitor they in service to, even if they do not personally agree with those orders.
They have to be highly trained. They face the darkness of Chaos and deamons that most of the Imperium is kept blessedly ignorant to. They are not mind-blanked, personality void warriors but astartes warriors with their own powerful personalities whose's souls have been tempered and warded to the point they can face the greatest fiends that the warp has to offer. A great example of them in current cannon is the BL novel 'The Emperor's Gift' by Aaron Dembski-Bowden. Each of the Grey Knights in the story has his own quirks and personality, infact one could argue that their personalities have to be stronger than normal space marines just in the aspect of what they are and what they face.
The Grey Knights don't typically 'work' with anyone, as their very existence is kept as a closely guarded secret. The Grey Knights are beholden only to the Ordos Malleus and to the Emperor himself. Even to other chapters of Astartes they are an enigma, at most they are known only by the chapter masters and highest leaders within the chapter. I think the one legion that knows about them openly is the Space Wolves, and the reason for that is what the novel I mentioned above is mostly about.
Just knowing about the Grey Knights/catching a glimpse of them on the battle field has seen entire guard units mind scrubbed/killed.
Would the space wolves come to the aid as they crash down in their own back yard? despite them being a successor chapter to the dark angels? Or would the dark angels respond to a distress from them? I can see the grey knights coming in on this because well. Kind of their job. Or hell, This could land in the back yard of the Death Watch. So you have an Inquisitor leading them.
If they crashed into Fenris they would have some explaining to do (those few astartes that actually survived the crash and then survived Fenris' warm
welcome that is).
You have to remember that things in the Imperium aren't fast. If they get a distress signal out, if there is anyone within range to pick it up, if those in range even can respond- it might take weeks, if not months for any kind of would be saviour to respond.
The Galaxy is the backyard of the Deathwatch, they are specialized teams drawn from loyal chapters and sworn to the service of Ordo Xenos for an amount of time before they are allowed to return to their parent chapter. Those astartes are oathsworn never to speak of what happens or what they witnessed in their service to the =][=, even to their brothers. Unless you are talking about the half of the ship that crashes into a planet (which would kill almost everyone on that section of ship by the way other than maybe some of the astartes) which has a Deathwatch Watch station or Watch Fortress. But you are talking about the possibility of random astartes from around 30+ chapters that send warriors to the Deathwatch that might be present. An Inquisitor would not necessarily be 'leading' them per say, they would be acting upon orders from an Inquisitor but that doesn't mean that they actually are physically led by one.
Basically, what I was interested in is to be a member of that Grey Knight team that is scouring the torn remains of this warp-tainted ship and saving/deciding the possible purity of those who remain.