At its dead heart, the planet's every artifact is switched off at once — the defense grid, the swarming machines, the network all fall silent as Elvi carries Miller's core through the dead spot.
Ilus/New Terra, the engineered power station, is switched off from within. In its control-center 'nerve cluster' — hundreds of niches of waking machines and swirling firefly motes around the lethal 'dead spot' — Miller connects to as much of the planetary system as he can and, with Elvi's help, drives it all into the darkness that kills such networks. When Elvi carries Miller's final blue core through the dead spot itself, the whole world goes still: the knife-limbed machines freeze, a million tiny silver mechanisms fall dead at once, the chittering and booming cease into total silence.
The defense grid that had damped fusion in orbit and dropped the ships toward reentry is dead; the artifacts lie inert. The dead spot itself, however, remains — the bright-bordered structured darkness the builders' killers left behind, untouched and undiminished even after being used, still filling Elvi with 'a deeper dread than' anything she's known. The planet's two-billion-year machinery is finally, fully off.
Below the storm-clouds, the alien plant now a graveyard of dead machines — still knife-limbed claws, silent conduits, drifts of switched-off silver mechanisms — lit only by a hand terminal; at its heart, the dead spot still swirling black and bright.
The alien world and setting; here switched wholly off — defense grid and all artifacts dead — save the enduring foreign 'bullet' of the dead spot.