Erica Messer, the showrunner of Criminal Minds has suggested that they might bring back "familiar faces" in season 11.
As for prospective candidates other than Paget Brewster, who portrays Emily Prentiss, there is Elle Greenaway, played by Lola Glaudini.
Recently, Joe Mantegna (David Rossi) confirmed that Brewster will be back in the next chapter. Prentiss also guest starred in the CBS procedural in season 10, so that wouldn't necessarily mean an old cast member being brought back. Prentiss hasn't been on the show since after the second season, when her character resigned under embarrassing circumstances. It would be interesting to see Greenaway return as she is the only other old mainstay that could have a shot at a comeback. The other old cast member would be Mandy Patinkin, who portrayed Gideon. Not only did Patinkin have a bad falling out with the creators of the show but his character was killed off in a flashback sequence in season 10.
Here's Messer's quote from an interview to TVGuide hinting at bringing old characters back in the next chapter:
"Because it's Season 11, we want to focus on them a little bit more. That's why I think it might also be a good idea to leave [the position] open so we don't have to spend time introducing a new character for fans, but really dive into these people we've known and loved for 10 years. I think there are also conversations to be had about people who have come and gone in the past 10 years and bringing people back. It's just the acknowledgment of this is what happens after 10 years of working somewhere and people do come and go. It's like what we did with Gideon -- in that case and writing to the reality of that. I think we'll be seeing more familiar faces next year."
The finale of Criminal Minds aired on May 6.
Watch the preview: