Show me a nano-anything that could, once arriving a billion light years (name your distance) away from this planet that could have the energy to transmit a damned thing back to us.
There is the familiar Friis Transmission equation and the N=kTB formula that they are going to have to deal with, and even under 0K and subcycle bandwidths the problem is hopeless IMO.
Time, bandwidth, noise and noise figure are all variables in what I call TANSTAAFL. Even with infinite gain with zero noise figure, the bandwidth would be so small it would take ages to send back.
My initial thought, as well. It seems that this would have to be the space-age equivalent of a “message in a bottle” that would have to rely on someone to reply. (Not sure we want to do that...)