I just hope the Swarmlord did die on the Ultramarine homeworld. While it could be an interesting that it survived and burrowed underground, it risks the chance of it recognizing Papa Smurf as his spiritual liege.
I like how you made it dark enough not to see any markings. It could well enough be any marine sitting with a bloody stump of an arm and a bolt pistol and still be confident he'd make it out in some form.
I have to say that, being a 40k fan (mostly of the universe and the mental-artwork that in conjures up) that this is absolutely amazing. It captures the atmosphere of the marines last stand. Also it fits in exactly with my own personal mental picture of what I imagine something such as that to 'look' like, from a mythical directors position I suppose.