He was mentioned to have a new assignment dealing with the Phantomhives so it's possible. Also he's one of Yana's favorite, she's definably bringing him back.
I agree with vamp_grl_123. Ronald mentioned an assignment Grell had dealing with the Phantomhive household, so... there's just not much 更多 to it than that lol. It's not unlikely.
I agree with emiliux123. He's there with Ronald Knoxx collecting souls from people eaten 由 zombies! Yay!!! Anyway 你 will be looking 前锋, 期待 to the point when Grell sees Sebastian is there! Like Grell says, the purest form of 爱情 is a death match! XD