'Are you alive?' is used when you haven't spoken to someone in a long time. It basically means 'long time no speak' just a shorter way to start a conversation.
Jeri: Heyy! Are you alive? Megan: Yeah! Long time bae how have you been?
.....
Ronnie: Are you still alive?
Emma: Yess but you anti-snapbacked me and now you text me!
Emma: K.
