Why she might be dead: Maggie's health is on a steep decline in the finale, and as she quivers in front of Negan, the leather-clad villain offers to put her out of her misery. Glenn immediately leaps to protect her, and even though no one dies, the moment between them is a total punch to the gut. It's just a taste of what actually goes down in the comics (Negan kills Glenn, Maggie loses it, everything is horrifying), and puts their beloved relationship on display. In the Comic-Con footage, there's also a close-up shot of the bloody, pulpy carnage of whoever is on the receiving end of Lucille, and within the red goo is an engagement ring. Could it be the one Glenn gave to Maggie? Sure seems like it.
Why she might not be dead: It's safe to say Maggie is not Rick's "right-hand man," although she is kneeling directly to his right. If she's the one to die, wouldn't Rick be covered in more blood? Also, the comic book version of Negan has an aversion to killing women and children, so murdering a pregnant woman like Maggie seems like it wouldn't be his style regardless of who his "moe" lands on.