Creatures with indestructible are meant to move to the graveyard when their toughness gets reduced to 0 or less. I used meathook massacre on a 2/0 token that was protected by tamiyo's safekeeping. It's stats were reduced to 1/-1. It should've moved to the graveyard as a state-based action. This can be reproduced as needed by reducing a creature's toughness with a -x/-x effect after the creature has been given indestructible. I didn't take a screenshot but it's easy to reproduce.