He chose a floor where a floor laying crew was working and where boxes were piled high to one side. He created a nest of sorts with the boxes. He did fire with three TSBD employees directly under the window from which he was firing. I don't think he "quickly snuck upstairs" or "realized he had a chance." I think he was in place with sufficient time to carry out his act. I don't think it would have made the slightest difference to him if there had been employees on the 6th floor. Once the decision was made, he was going to shoot JFK, period. What he would have done after the shooting if there had been employees up there - shoot them (I doubt it), shot himself (unlikely), left the floor brandishing the gun (possible) - is anyone's guess. He may have carried the rifle as far as he did precisely because he wasn't sure he was alone. Nothing about the circumstances suggests to me the mindset of "I'll shoot JFK only if the coast is clear and I have a realistic chance of walking out of here alive."
What he would have done after the shooting if there had been employees up there - shoot them (I doubt it), shot himself (unlikely), left the floor brandishing the gun (possible) - is anyone's guess.
This is an interesting conundrum, I've speculated in the past that Oswald crossed the floor with his rifle just in case he came across another employee who was stopping his flight from the scene of the crime, but there is still questions and further speculation.
• Why didn't Oswald just leave the rifle in the sniper's nest because if he did come across another employee on this floor he could have kept going and just mumbled something like he did with Reid?
• Did Oswald leave the rifle at the opposite side of the floor to delay it's discovery and hence give him more time but would an extra hour or so make a real difference because the shells in the sniper's nest were already a bit of a give away?
• Why didn't Oswald take the rifle down the stairs but I guess if he was discovered by the cops this would mean instant death.
To me the first option seems to make the most sense, just get the heck out of there and leave any immediate connection far behind?
JohnM