User blog comment:Paul.rea/Teen Wolf News 020117/@comment-24715512-20170205120124

"a different source in the production confirmed to TWN that Dylan O’Brien will return in some capacity. Davis says MTV won’t let him give you the exact status of these and other returning actors yet. “I will tell you that more people than I expected are showing up to say goodbye to the show,” he reveals"

That could be anyone, Danny, Kate, Braeden,  Meredith, Brett, Deaton,  Gerard Argent,  etc, etc literally any past cast member whose character isn't dead. Neither Davis nor MTV have CONFIRMED O'Brien's return or that of Haynes, Hoechlin or Sharman but they are pretty quick to announce other cast members, so why not O'Brien? It is in their interests to keep hope and speculation alive amongst fans, especially given to poor overall ratings of 6a and this show has an unfortunate track record of baiting and misleading fans.