Without being there, and even then, it is almost impossible to know exactly what happened; however, since you found your arrow intact, I don't think you got a gut shot. You may have actually hit him in the hip area. That would explain the lack of penetration and the arrow falling out. In that case, you can hope that no major artery was hit and that he will heal up. Since you've looked and looked and looked, the only thing left is to watch for buzzards circling. If you see some in the area, you might try to find what they are after. It might lead you to him if he died.