Sometimes they run rampant anyway.
In my most recent session one of the PC was planning to assassinate an important noble. He tricked another PC into arranging a meeting w/ said paranoid noble. When going through the Noble's security our would be killer was picked out by the nobles security psyker (who used soul sight and rolled high enough to read that the particular character had malign intent toward his mistress.
As a result of this that character was separated from his ally stripped and locked in a basement cell to await torture. Alone and facing certain dealth the PC pulled the bone knife he had hidden in the concealed pocket in his chest cavity. (He had the talent, and fooled the weapon scanners by having a weapon w/ the density of bone concealed up against his ribcage)
So he pulls a knife on the psyker, kills him, then proceeds to murder his way through the nobelwoman's security force, stealing weapons and armor along the way. Starting with a bathrobe and a knife 1 character proceeded to massacre 28 enemy troops, all with higher WS, BS, S & T than him, five of whom were in power armor.
How did he do it? 3 things - 1) has the talent that gives higher AB for purposes of initiative and always went first, 2) is a void born who rolled 3 FP at character creation, then rolled +1 FP on emperor's tarot, 3) for six hours of game session, all in vicious combat, he rolled higher than 20 maybe 1 out of 5 rolls. Sheer defiance of any mathematical probability.
I can't say I was trying to kill him, just trying to realistically model security force for the target he was trying to kill. Never expected him to attempt to single-handedly murder the entire facility....much less to succeed. Luck can do crazy, crazy things.