At least one person from Jim Schwartz's coaching staff has been retained by Jim Caldwell. According to Tim Twentyman, the Detroit Lions have elected to keep special teams coordinator John Bonamego, meaning he will serve in that role on Caldwell's coaching staff.
Bonamego joined the Lions last year, and it's probably no coincidence that the team's special teams units were much improved in 2013. They did have some issues with allowing kicks to be blocked, but their coverage units were fantastic, Jeremy Ross emerged as an outstanding returner and Sam Martin really helped upgrade things at punter.
There is also a report out there (from CoachingSearch.com) that the Lions have retained running backs coach/run game coordinator Curtis Modkins and assistant defensive line coach Jim Washburn. That's unconfirmed, though, and I tend to think that report confused which Washburn is staying based on this:
Andy Moeller has talked to Jim Caldwell, awaiting word if there's a spot for him. May not be as Lions expected to retain Jeremiah Washburn— Aaron Wilson (@RavensInsider) January 16, 2014
One other piece of news: Offensive assistant Kyle Valero has not been retained.
Saw offensive quality control/assistant WR coach Kyle Valero in the hall. He said his goodbyes as he hasn't been retained.— Tim Twentyman (@ttwentyman) January 16, 2014
Considering that news is already starting to leak out, I would expect an official announcement on which coaches have been retained relatively soon.