Who did the Apostles Peter and Paul have to give account to? They both had to explain themselves to the church at Jerusalem and Paul also had to explain himself to the church at Antioch. Why? These two churches appear to have been the largest churches in the Book of Acts. The Jerusalem church was dominated by Jewish converts, while the Antioch church was dominated by Gentile converts.
They were both large, successful churches led by soul-winners, and they made the right decision about Peter and Paul.
But that isn't who modern missionaries give account to. They often have to give account to a mission board that has no Scriptural authority to exist. And there's someone else that's even worse.