The problem with drones in that role is the communication system. The Russians and the Ukrainians have been using jamming systems with very good results. I really believe that we will come up with jamming systems which can knock an ICBM out of flight.
Very powerful jamming systems will send all this back down to the individual infantry soldier carrying their weapons on their backs to put boots on ground. (Kind of like the Apocalypse says that each man will be fighting with his own weapons in Armageddon.)
Doubtful. Most ICBMs are designed to launch and then use inertial navigation to deliver their warheads to the dropoff points. Very difficult to jam that.