According to Jack Pendarvis, who voiced Root Beer Guy and wrote the character's death, he was killed off to provide an explanation as to why the Banana Guards remained so incompetent despite his leadership.

Who plays Rootbeer?

Plot. Root Beer Guy (voiced by Jack Pendarvis) is a candy citizen with a dead-end job; as a method of escapism, he often tries his hand at writing a crime and detective novel. One night, while working at his typewriter, he oversees Finn and Jake kidnapping Princess Bubblegum.

What is starchy in Adventure Time?

Starchy (sometimes reffered to as Starchie or C3591-F in Graybles 1000+) is the Candy Kingdom's residential gravedigger. He first appears in "Slumber Party Panic," in which he is frightened by a Candy Zombie and suddenly explodes while delivering a larger corpse shovel to Princess Bubblegum.