I read this on the web, don't know if it's confirmed or rumor:
"Janice isn't leaving the show because she wants to. Peter Hamm won the battle and therefore owns the rights to the name of JDMA now. Furthermore, any models who were signed before Janice fired Peter were under "Nouveau Model Management" where Peter is CEO. He legally owns the all the models up until the 4th season. The other models are signed under Janice's new partner. The show doesn't have legal rights to the name anymore which is why the next episode will be the last."