Is there ever a reason for which a pastor should not be eligible to return to ministry?

I was reminded this week of an incident that happened at a church in our city a few years ago in which a pastor lied to thousands of people in his church and received money under false pretenses. My thoughts led me to consider whether or not he would ever return to the pulpit and if he does, should he? Although I believe God forgives and is able to restore a person to wholeness, I wonder if there are some abuses (including but not limited to sexual abuse) in which a person disqualifies themselves from ministry. This was not a guy in bad marriage falling for a pretty young girl (which is bad enough). The influence of the matter was widespread. In my mind there are certain abuses that should exclude people from the pulpit but I wondered what others believe?

I think for instance of evangelists & pastors who have fallen and then disappeared for a short period of time to only reappear claiming healing and wholeness. All of a sudden they start new ministries claiming to be ministering to those in similar circumstances. In my mind this simply seems far too convenient. I am sorry but these people have abused their positions. Abused their people spiritually and abused, in a sense, God. God does not need them. He can call others and their need and desire to return to ministry so quickly concerns me. Perhaps I am being too harsh but I think it is better to be safe than sorry.

I wonder, what do people think: What instances (apart from the obvious) exclude a person from ministry and what must a person do in order to re-enter ministry?