I don't remember it ever taking close to a week to build one building or to have a few days with no active building up.The team has adjusted the amount of resources needed to rebuild the buildings, so the rate buildings are rebuilt is about the same as it always has been.
Why should anyone care about these buildings in a future expansion? You are removing the Mage Tower appearances...The buildings should always remain reasonably functional, they won't make it take months to rebuild the buildings in a future expansion.