While you may lose Units and Resources if you fail to defend your Castle, no building can be completely destroyed by enemy attacks. However, some objects may be damaged during successful attacks and may need to be revived or Upgraded. The repair will take no more than two hours.
Remember that the Altar of Weor is different to all of the other buildings. When it is damaged, all of its Upgrade progress will be lost and it will return to Level 1. However, Upgrading the Altar of Weor is free and you can gradually regain its Level.