I believe Stephany was already dead at least a couple of hours before he went out for coffee.
I believe that between the time Stephany entered the hotel room, and the time he went for coffee, he had already beaten her to death, showered and changed his clothes.
He went for coffee to check the atmosphere of the hotel (make sure no one was acting suspiciously), and then I'll bet he went through Stephany's car, looking for what he could steal from it, and see if it would be a feasible way for him to get out of town.
He then went back to the hotel with two coffee cups as a ruse to make it appear that both of them were still alive, when in fact, only he was still alive. I'm sure he was very aware that he was being recorded by surveillance cameras.
He then went back up to the room with the two coffees to take one last look at his 'handiwork', and to gather the bloody clothes, hoping to clean up the room a bit. Once the task of 'cleaning up' proved to be too formidable, he simply gathered the items he wanted to take, and left for the last time.
(I'll bet if he had a camera- or a cell phone with a camera- he took/ would have taken a picture of her dead body- which the authorities would now have).
Anyway, I believe that Stephany was dead before he left under the ruse of 'getting coffee'.