You're actually right, Imu doesn't leave until the next chapter.
Still, Imu should have either handled it himself, or simply DR'd more people if he was going to leave. He came to Gv and didn't really accomplish anything besides breaking Xebecs spirit
Tbf, the destruction of the Davy Clan (and as you said, breaking theit spirit) was the only thing he was even there for. And he DID do that. He presumably DR'd all the other Davy's (because we have never seen anyone else do that, and Imu himself was seemingly manifesting through Mars on Esperia, which is the only other place we have seen it done. So he probably just did it through Saturn or something on GV), then went after Xebec, then made him kill his own wife and child (which, as far as he was aware, he succeeded; and kinda hard to predict Kuma from the top rope saving them in the exact moment Xebec was about to kill them).
Everything else was a bonus at best, and Imu didn't particularly care. Which is understandable, as I am SURE he has seen many different people over tbe past 800 years who were comparable to the big names of that era, and they never amounted to anything. So him thinking "Well, it would best if they all died, but ultimately it doesn't matter" is not really a bad take. With hindsight, with these SPECIFIC people it was, but Imu is acknowledging that in present day. 🤷♂️
