In the tale there is a limitation for travel with the human being onboard: top speed is lightspeed.
And in the very end Rocannon has to wait for his comrades for 8 years (why they are flying to recover him and he actually died waiting for them). But I think they could just sent for him an empty space ship flying at infinite speed, and then fly back "slowly" (at lightspeed).
Was there any explanation – why this couldn't be done ?