In risk terms, the satellite that was ditched is worth absolutely nothing compared to the ISS. The ISS is the single most important thing humans have in space at the moment.
Purely on the basis that the new trajectory can't be gone over with a pin, even if all the maths comes out saying that everything is lovely, you do not refire an ISS delivery rocket that is not where you expected it to be, especially one that has already sustained damage, just to test a new robot.
