When Negan swanned into town in "Service," he was ready to start his psychological torture of the Alexandrians all over again. It wasn't enough for him to steal more than half their supplies — he also wanted to taunt his victims. Most of his attention was focused on pushing Rick to the edge, but he also took time out of his busy jerk schedule to be nasty to whoever crossed his path. He even made sure to ask about Maggie, with a lot of crass commentary to go along with the question. However, he was told that Maggie was dead and was even brought to her grave for proof. But is Maggie dead on The Walking Dead?
It's true that Maggie is nowhere to seen for more than half the episode, but it's important to remember what she was up to the last time she was onscreen. Maggie was suffering from unspecified pregnancy complications when the entire group was stopped by Negan and Glenn was killed, but she still needed help after that. The plan was to take her to Hilltop where there was a doctor who could care for her, and Sasha promised to take her at the end of the premiere. Considering Sasha is also MIA during "Service," it's more than likely that she and Maggie are at Hilltop.
But why come up with the the fiction of passing her off as dead? That one's easy: it's for her protection. The fact that Negan killed her husband makes her a particular target because Negan likes to get very personal with his victims; it's part of what makes him so cruel. That's proven when he makes it clear that he's interested in her, even saying that he was planning on trying to take her back with him. This fits Negan's pattern when it comes to choosing his "wives," at least from what fans know of him and Sherry. Intimidation and harassment are his techniques, and Maggie is particularly vulnerable right now.
Maggie being alive is practically confirmed in a conversation between Rick and Gabriel, though it's not stated outright. But it seems the plan was actually Gabriel's idea and Rick thanked him for his quick thinking. Gabriel told him it was nice digging a grave that he knew would stay empty, implying that Maggie is fine. It's all about protecting Maggie and keeping her out of Negan's way.
The episode ended without Maggie appearing, but rest easy: she's in the promo for the next episode, alive and (hopefully) well.