No, it's Zack and not Sweets. The writers are moving on with the storyline overall. They also made it Zack because they wanted to "shake up the cast". I think they just wanted to copy House, have a new group of students follow Bones around.
However the actor that plays Zack seemed really happy and upbeat during an interview with TV Guide. He seems to be in at least part of next season and said he blows up and is in the hospital next season. Turns out he is in the crazy hospital.