Haley and Cardinals coach Ken Whisenhunt have been friends for years, and Haley was offensive coordinator in 2008 and 2009 when the Cardinals won consecutive NFC West titles.
It's unknown what title Haley would have should he return to the Cardinals, but he likely would be placed in charge of the offense again.
The Cardinals have not been nearly as good on offense since Haley left, but his departure also coincided with the retirement of quarterback Kurt Warner. The Cardinals have had four different starting quarterbacks since Warner retired.
When Haley left, Mike Miller was promoted from receivers coach to passing game coordinator. Russ Grimm was assistant head coach/offensive line and run game coordinator. After that season, Miller was promoted to offensive coordinator, while Grimm remained assistant head coach. He continued to have a strong influence on the offensive game plan.
Whisenhunt would have to create a position for Haley, which would mean either re-organizing his existing coaching staff or adding a coach