Oh, that's not good. Depending how far he got the fish down he could have lost very precious stomach fluids. If you decide to keep it give him 14 days before you try feeding it to be safe. Feeding to soon after such an incident can just make things worse. Then if you do feed it give it a smaller meal first.
That's really impressive he downed that bass. He sent it back up because he is going to fight or flee when it gets the chance.
I promise a captive bred and born snake will be a much better pet for you. You seem to have the setup so why have you not bought one yet?