Depopulation is not something you'd associate with a major city; they tend to create their own buzz. In the case of Christchurch, in the wake of the earthquake, we might be seeing more of a dead cat bounce. The city will of course recover, but one is reminded that the series of earthquakes was not the only reason they left....it was just a timely excuse. Prospects are far better in Australia, and NZ'ers are voting with their feet.
In 2012 there ought to be a construction boom in Christchurch. The problem of course driving many people away is:
1. The prospect of more earthquakes
2. The cost of rebuilding
3. The unmet demand for labour, forcing up costs
4. The excuse to leave, e.g. The wage differential with Australia, stagnant growth in NZ