Keith did as Lexi instructed. He brought their bags with them and went out of the building.
While exploring earlier Keith was able to locate the security room where the security guards can see the live feed of the cameras. Although terrible, the cameras are placed on good angles that let them see the most of the rooms they are monitoring.
Lexi has the tracking map in her hand. While Keith wanted to have it with him, he let her do whatever thing she is doing with it. He's already familiar with the layout of the buildings anyway. And have also remembered which room or corridor has the camera so they should just avoid it. So if Lexi turned to a corridor where a camera is, he could just pull her aside and go to different direction.
Lexi walked in the front while Keith silently followed behind. They walked through narrow stairs and was able to get out of the building.