I find it implausible to believe that anyone in charge of the evacuation planning for the WTC complex would EVER consider either of the twin towers a safe place to be in the event that one of the two collapsed in a controlled fashion, much less the way it did in fact collapse. Remember that we are dealing with potentialities in this scenario and one of those potentialities is an uncontrolled collapse of one tower knocking down the other.
None of this hinges at all on whether or not a second plane enters the picture.
Sure it does. Before that, there was only a big big fire in the other building, and debris and bodies hurtling down at high speeds. The building was still standing, as advertised. They weren't anticipating a collapse. If they HAD, they would have ordered an evacuation.
After the second plane, both buildings were on fire and Tower 2 was in much more trouble than Tower 1, havng been hit much lower down. That's the reason it would have been the right thing to evacuate immediately. But that would require foreknowledge they didn't have. I'm sure SOME people in the city (architects and engineers) realized at once what was going to happen to the buildings after the planes hit, but I don't think it's reasonable to assume that the guys in the WTC command center did. That's all.
But, I'm sure we'll hear much more about it during the court cases.