Was also thinking maybe there can be 2 types of demolition:
1. A fast demolition where all resources invested to build the infrastructure would be lost (good when the enemy is near)
2. A slow demolition where you get back some resources (good when you've got time)
This would expand the strategic options.
Also demolition should stop (with infrastructure partially damaged proportional to how long the demolition process was going on) if the enemy capture the province before demolition is complete.