Well, after finally reading through this whole thread I'm surprised I didn't see one thing;
You said that you must cross the first skybridge at the 25th level because the 26th is blocked off by rubble, right. But that's one thing that really shits me in games and movies; the floor that is blocked off in buildings is always the one that has the escape route on it.
So, basically my suggestion would have the 26th or 27th floor being the last ones meaning that the group has to get back to the skybridge.
I've never been one for enjoying the ample 'conveniences' in the horror genre.
Just an idea
