The diorama reminds me of the excellent film "Casualties of War", which does also hint at rape in a rather extreme way, without actually showing the crime in a pornographic manner.
The conflicting feelings and interpetations this piece evokes make it so great in my eyes
Gangrape is the moste likely outcome, but it is NOT the only one, as others have pointed out. There are so so many films that play with the notion of impending rape only to have the tables turning and the aggressor down in his own blood.... Kill Bill, Sin City etc (hell, even "sailormoon" or "alice in wonderland" contain more or less hidden rapetreads to the heroines). I don`t like all of them, but they are more or less deemed socially acceptable or even "fun".
All those border on the pornographic, because the heroines are depicted as good looking, sexy, alluring etc. (as is this eldar, which is kind of a miracle in it self, because she is a 28mm piece of plastic!) but thats part of the appeal (for me at least): You must not feel what the rapist feels, but you can understand why doing such an act might be attractive for a depraved man.
The diorama shows something I can emotionally relate to on many levels. All this grimdark stuff about eternal servitude to the dark powers/ god emperor, the depravities of slannesh and the dark eldar, whole planets destroyed to get rid of a single infected person, space marine training which leaves 3/4 of the aspirants killed, broken ore maimed etc. all that is not a single ounce better on the moral scale, but (to me) much lower on the artistic scale, because it is so over the top I can`t relate to it.