What happened to the rebel Sheba son of Bichri at Abel-beth-maacah?

Answer: His head was thrown over the wall

A wise woman of the besieged city persuaded its people to cut off Sheba's head and throw it to Joab, saving the city.

“And Joab’s troops came and besieged Sheba in Abel-beth-maacah and built a siege ramp against the outer rampart of the city. As all the troops with Joab were battering the wall to topple it,”— 2 Samuel 20:15 (BSB)