Here's what happened:
* The Secret: Mr. Winkler is revealed to be a member of a secret society called "The Order of the Ancients" who are trying to retrieve a powerful artifact called the "Eye of Horus."
* The Escape: Mr. Winkler is captured by his fellow Order members for betraying them and being suspected of stealing the Eye. He's then imprisoned in a secret underground chamber in the house.
* The Rescue: The Anubis House kids discover Mr. Winkler's imprisonment and help him escape. He then goes on to help them protect the Eye from The Order.
* The Departure: After the Eye is destroyed and The Order's plans thwarted, Mr. Winkler leaves Anubis House for good. He is last seen driving away in his van, presumably going to start a new life.
The official reason given for his departure is that he was going to "find himself," but there are theories among fans that he might return in later seasons. However, he never appears in the series again.