The Holy Spirit's departure from Saul was not about salvation but about losing the anointing to be king — the Spirit empowered Saul for his royal office, and when he repeatedly rebelled it departed.

Mike distinguishes the Old Testament mode of the Spirit (empowerment for a specific office/task) from the New Covenant indwelling that accompanies salvation. Saul's case is the royal anointing being withdrawn, not a salvation statement.