My god, they've taken the ... that I've got to get to!
The card text says


  Play this card at the start of a Zombie Turn on any Hero and roll a
  Random Building.
  
  That Hero may not search. Discard this card when the Hero moves into a
  space of that building. If the Hero is already in the building or
  cannot enter it, Re-roll.


Your scenario renders the hero unable to enter the building, so a re-roll is required.

This is confirmed on a BGG thread by an answer from the game designer:


  If the building is made unavailable to the Hero, then you must re-roll to determine a new building for the Hero to get to.