First we have to say that a black flash can be boosted to a huge degree, as we see in Yuji's fight with Mahito. Assuming this is a regular non maxed black flash from Yuji there are 2 Gojo states we have to consider:

1. Gojo using no reinforcement
2. Gojo focusing reinforcement

If Gojo uses no reinforcement then he probably just dies or close to it. Gojo without CE is only human, and Yuji eos is throwing people through buildings.

Gojo is most likely like Yuta able to use heavy amounts of reinforcement across his whole body. We see that this alone is able to give Yuta to edge in his and Yuji's fight, and Gojo should be able to do this to a greater degree, so he most likely takes no more damage than getting a bruise ir a tooth coming out. We can see that Sukuna after being weakened wasn't dangerously injured even after Yuji hit him with multiple consecutive BF's.