Emergency disembarkation

Blocking the access point(s) of an enemy transport stuck between a 3" high building and with a unit of models surrounding the other sides within 1" of all sides (movement) and the transport is subsequently Wrecked (shooting) -

   The passengers must immediately disembark in the usual manner, save they must end wholly within 3" of the vehicle rather than the 6"  If, even by performing an emergency disembarkation, some models are unable to disembark  are removed as casualties. This does not prevent the rest of the unit from disembarking. Pg 215 BRB

   The rules for emergency disembarkation then goes to say that enemies that choose to E-Disembark that cannot place all models in a unit have the unit removed and cannot take voluntary actions, so I believe that would go to include overwatch or Go To Ground provided the Pinning test passed.

Question is 1. would the Building now qualify as impassable to the passengers or 2. could they climb the 3" vertically and be placed on the roof level without a surface directly above the position in which they are in base contact with the hull. I'm looking at the image on pg 32 BRB about the surface on which the marine climbs to. This is just for the sake of figuring out LD tests or VP gain instead.