The bridge was originally planned to be rebuilt, but before it ever reached that stage GD had grown to the point where the bridge would have given a quick exploit to reach the dungeon on the other side, so it remains an unrepaired and unrepairable bridge. 
Cronely wan never intended to be optional, the problem was as there was more than one direction to go some people would forget about the other direction and then never find Cronley, hence the change of the map areas to prevent people being able to miss one of the story line dungeons.