u/Pcat0

From the text of the book, it seems very likely that the local galactic neighborhood is absolutely chock-full of life, a lot of it potentially intelligent. As Grace and Rocky conclude, their species both needed to be at the same relative technological level in order to be able to, and need to, make the trip out to Tau Ceti. But that would also imply that there is a lot of intelligent species in the local galactic neighborhood that just wasn't at the right technological level (or just didn't decide to make the trip). That also tracks with the hypothesis that both Earth and Erid were seeded by the same ancient interstellar microbe from Tau Ceti. It would be very easy to believe that the microbe would have also made it to other star systems.

Knowing that there may be many planets full of life facing mass extinction events, both Earth and Erid may feel a moral obligation to spread the cure to the Astrophage crisis across the galaxy. It would be very doable. An army of beetle-like probes containing a Taumoeba farm could easily be built and sent to each of the local infected star systems. The probes would just need to find the Petrova Line once they got near their target star and then crash into whatever planet the line was connected to. The probes could even modulate their thrust during their deceleration burn to attempt to announce their presence and communicate with any intelligent species watching their skies. A new super Taumoeba strain that is tolerant of a large variety of atmospheric conditions would need to be bred, but that is doable with a planet's worth of resources.

I think the Eridians would likely be in a better position to conduct such a mission, and while they would need to build up quite a lot of computer technology first, humanity would probably have a longer road ahead of them rebuilding society before they can start building interstellar probes again.