I'm not entirely sure who 'Alex' in relation to Keemstar specifically is without more context. Keemstar is known for his work in the online content creation and streaming world. Maybe Alex was someone he collaborated with, had a feud with, or was part of a particular event in his career.
I really don't have enough information to tell the full story. It could be that Alex was a regular viewer who had some sort of significant interaction with Keemstar, like winning a contest he hosted or getting involved in a charity event he organized.
Michonne does die in the comics. The circumstances surrounding her death were quite dramatic and had a significant impact on the story's progression. It happened during a major conflict with other characters.