The low altitude economy drones would only be useful for detecting ground troops. To fight those ground troops, you would need MANY combat drones, and those would need to have their own logistics chains even if some commonality exists. To deal with stealth aircraft and missiles, you would need dedicated AW&C and combat drones, which would have to somehow cover the ENTIRE chinese borders, including valleys and mountains.China is at this very moment planning the servicing, maitenance and operation of millions of drones. It is called the low-altitude economy by another name. Of course it is possible, use your imagination blud. Drones can recharge themselves by flying back to base. Drones can diagnose themselves and any faults could be repaired robotically or they can just fly straight to the recycling centre. Do you honestly believe that in 10 years time none of this would be possible?
Also why are you talking about ballistic missiles? That's a problem whether China extends its borders by a few hundred miles or not.
I am talking about ballistic missiles because China would then have to deal them coming from the north and northwest as well, instead of Russia helping intercept them and retaliating on those who launch them.