How much daily human input is needed to keep GPS satellites and service operational?

I'm wondering if in the event of a massive natural disaster or disease pandemic how long would your basic handheld GPS unit still be functional. And also how would this affect cell phones or are they totally separate.|||1) cell phones usually get assistance via the wireless network, so they may be challenged in acquiring GPS satellites


2) how long will GPS still work? accurately about 1/2 year - after a few days, the satellite constellation works without ground support - if things are in pandemic state, other issues will be more important - just think about what means you will need to protect your food supply from your hungry neighbors