Don’t see why it couldn’t work. The only things with physical wear and tear are the electric motor and the bearings. No reason they can’ make a motor or bearings that will last five years.
I think the five years lifespan is probably based on battery efficiency. After five years, the battery won’t be able to hold enough charge to keep the drone up over-night.
Looks feasible to me and a lot cheaper than satellites. The only downside is it makes full time surveillance too easy.
Motors and bearings probably won't run full-time. Operational strategy would likely be to glide most of the time, and use motor/battery to climb back up to reach the next glide point. Same strategy as already used by oceanographic "drones", which are designed to sample the ocean for various parameters autonomously.
Tens of thousands of parts...how many are critical to safe flight?. Agree electric motors are highly reliable, but there’s a lot of critical flight safety parts besides them. Of course, many of those failures will lead to degraded flight and most likely a safe landing for maintenance.
Still, keep your eye peeled for falling drones.