If there is still no repentance, then the matter must be escalated further. Church discipline must take its course: ‘Tell it to the church.
The Lord’s direction here is very helpful to us in cases where people must be put out of the church. In 1 Corinthians 7:15, Paul allows desertion as a grounds for divorce (see notes on Mark 10:12). The rule is ‘if the unbelieving depart, let him depart. A brother or a sister is not under bondage in such cases.’ But what if the one departing is a believer? This passage in Matthew answers that question, and says that after due process and failure to repent, the one departing may be regarded as an unbeliever, and therefore the rule applies even in this case.