Replace the ODI meter with human population meter, showing the surviving population / initial population. The player loses if the human population reaches some low number or zero.
Protecting Havens will be more important. We will reduce the number of Havens in the world but make haven defense rewards more significant. Pandoran attacks on Havens will be increasingly deadly.
Mist repellers will be more important because we will increase the mist threat to human population attrition.
On higher difficulty, Pandoran research progresses faster which includes greater threats to the human population which makes saving people more challenging.
The population will affect Haven zones. Haven zones will stop functioning when the population gets low but the player will have an option to repair these zones. The zones will affect the Havens - for example repairing a training facility will help protect the haven and repairing food production will prevent population loss.