Maybe you miss the point, there are different levels of Pikuach Nefesh, there is direct Pikuach Nefsh, Someone is having a Heart Attack NOW , there there are people on a Ventalator who would die without it.
Then there is indirect or unintential cause of Pikuach Nefesh. Lets say there is no electricity and one day you need to call EMS and because there is no electricity you cant call EMS, BUT most times you dont need to call, but the one time you need to call, you really need to call and if you couldnt call, someone might die .
This is just food for thought.
Of course Doctors, Nurses , other vital Hospital employees would need to work.
Most people would not fit into these catagories