What happened to Sennacherib after he returned home?

Answer: His sons killed him

While Sennacherib was worshiping in the temple of his god, his sons killed him with the sword.

“One day, while he was worshiping in the temple of his god Nisroch, his sons Adrammelech and Sharezer put him to the sword and escaped to the land of Ararat. And his son Esar-haddon reigned in his place.”— 2 Kings 19:37 (BSB)