Stupidity: Why, in the most secure computer room you could find, with all those detection devices, did they not install video cameras? There is no risk of a security breach as they could be locked into a position that would not show the computer screen or keyboard but would show that an intruder had entered the room.
Stupidity: You would think if the security systems in the computer vault have to be off in order for a technician to access the computer then the computer itself wouldn't be accessible if the security systems were on.
Answer: I disagree with the other answers. I watched it in slow motion and thought he was going for the kill. There would be minimal struggle since Ethan isn't in a fighting position and Krieger was inches from his throat with the knife before he dropped it. He wouldn't care if there's a lock down because he would be out by the time they notice Ethan's body above. I guess blood spilling would give it away, but he'd still be out and under cover before anything can be done. He doesn't have to know who Max is or how to contact her he's working with Claire and Phelps. Luther wouldn't care too much because he just met them. At most all they have to say is that there was an accident and Ethan didn't make it. Max wouldn't care because she just wants the real list. If Ethan dies early the bad guys win and IMF will think hey he was the mole and got double crossed. There is 0 reason for Krieger to not kill him at that moment. He has the disc and that's all he needs.
Job as Jim lost confidence of Max. The deal was with Ethan. Ethan had to survive.