That's not a bad idea, Khalual.
I was considering having a shockwave of sorts damage their vessel upon the gateways activation, as per the movie, and then during the required repair period have them face illusions, nightmares and halucinations on their own. Perhaps have the less-than-puritan amongst them tempted by Dark Pacts, before unleashing some sort of demon or warp-creature from beyond for them to fight.
As I said, not a subtle scenario, but with some tension, paranoia and nightmares before a ultraviolent showdown at the end.
Another idea I'm toying with is having the station divided into sections which are separated by huge bulkheads which can't easily be opened while the power is off. Interior doors can be rigged by the tech-priests potentia coil, but for the bulk heads they'll need something else. Hooking up a portable generator, or wiring the doors to the ships reactor or something equally far fetched, I imagine. The point of this tedious exercise is that if the players decide to shut down the power again (a good idea) it won't be easy to escape back to their ship.
As they arrive on the station and make their way to the central core, they will find a dead man there. Suicide. So basically when the **** hit the fan, many of the mad scientist fled (and are hiding on the surface on the planet below, this being the fella they are looking for in the grander plot), while one poor shcmock had to stay behind to execute the poweroff while preventing backup sources from kicking in. Having achieved this, he was now stuck in the central part of the station with all the nasties from beyond. So he killed himself, and after weeks with no power and the portal offline, the warp-beasties suffered from instability and went back to wherever they came from.
Until some poor fool reactivates the gateway, of course ....
I want to present them with some hard choices. Shut down power? Well, who will stay behind and make the ultimate sacrifice? Blow the plant? That will burn the leads to their investigation, as well as pose immediate survival problems in trying to get home. Fight the monsters? What if there just keep coming more? Enter the gateway to destroy it from the other side? Heroic, but probably a bad idea...
I dunno, mostly ideas at this point, and I appreciate all sorts of ideas and suggestions from you, my collective evil demons of the interwarp