Cities Skylines Megadeth
The devil is in the details I suppose...
At its height my city had a population of approximately 54,000 when the Grim Reaper came a calling. The wave lasted quite a long time with my city bottoming out at 36,457 before I started to see a consistent uptick in growth.
That is almost 20,000 cims that left the building (pun intended) which created all kinds of issues. Instead of overreacting and spamming crematoriums everywhere I decided to allow those left behind to mop up the mess.
Some in the community think this is a bug in the game, while many believe it is the result of an overly aggressive zoning approach. With little to no tutorial in the game, it remains to be seen which the case is. When the residential demand bar is maxed out indicating very high demand for residential zones, you naturally create more zones to satisfy that demand. The problem is that creates a mass influx of new people who will for the most part mass die as well (rapid expansion = rapid death).
I eventually rebounded and obtained the highest city rating in game achievement.