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.
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.
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.
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.
Never Give Up, Never Surrender. for it is better to burn out than fade away.