The Dark Heresy group I'm running has managed to enlist the services of a large hive gang, consisting of roughly 400 people. They plan to attack the hive world's orbital docks in hopes of taking over the ship of a renegade noble house which is docked there, stealing the ship for themselves as a permanent mode of transport.
Here's the thing...
I rolled up a profile for the ship, a Vagabond Merchant Trader with roughly 30 Ship Points, using the Rogue Trader rules and basing it off of the resources the ship would have at its disposal. Taking the ships crew of 18000, I calculated how many relative "points" of Population the hive gang consisted of, as that's relevant to boarding. They have roughly 2 points of population, which means that within half an hour the ship is going to clean their forces.
The players in the group have previously snuck onto the ship and are aware that is has tens of thousands of occupants, along with dedicated barracks. I'm not sure why they think this is going to work, and so far I've made a point of not expressly supporting or denying this idea. Should I let them try, despite the fact that it's doomed to fail miserably? Should I ask for a Logic check on the part of the characters to suss out that maybe 18000 armed and trained arms men vs 400 hive gangers isn't good odds?
What would other GMs do in this situation?