Well, for the last 100 to 150 years the concept has been based on age value. What is the value of a place over time? One answer can be the age of it. In general terms, they say 40 to 50 years of age or so, because in the life cycle of a building that's when you need to start addressing things like replacing a roof or dealing with issues of the building envelope. However, in my world, in the private sector, we essentially treat these buildings from day one. The concept should be that you care for and maintain these buildings from the beginning.
It's called demolition by neglect. Essentially, someone doesn't take care of it for long enough and then it becomes an eyesore, a problem, or a health and safety threat, and therefore we demolish it.
The Eaton centre should have been protected and saved, just like any other property in an urban centre.