I really didn't get "Fatherly Spirit" from Aurelion.
He's an immortal.... thing, that for the most part, just cares about stars. He didn't seem to care about the common struggles of mortals, or even the struggles of other immortals. He only stooped to meet the Targonians because they were one of THE most advanced forms of life in the entire universe, and even those guys bored him eventually.
He doesn't care about the frozen watchers, or the sudden plague of undeath in the shadow isles, or even preventing normal death. Like he probably could just kill Kindred, but nah. In fact I didn't really get the feeling that he felt sad about killing other celestial beings, being that he'd rather kill them than watch more stars die.
Honestly if the Targonians didn't do what they did, I imagine one of two things would happen:
Void rifts quietly open on Runeterra and across the universe. Horrors spill out, billions die underneath a tidal wave of insatiable death bugs.
OR
Sol notices several planets infested with void abominations. Aurelion replaces those planets with stars. He likes stars better anyway.