In Episode 80 of the 2011 anime, they showed Gyro's back story then a clawed up chair. Was he killed or was he eaten? It wasn't clear what happened to him.
Gyro is killed and eaten after the Chimera Ants invade NGL.
but he is later reborn as a Chimera Ant... and the first to keep all of his human memories and break free of the Chimera Ant Queen's control.
The Chimera Ant King, Mereum, cannot be Gyro, because Gyro was shown leaving the hive at the same time that Gon was training to defeat Knuckle, in Chapter 204, before Mereum was born.
According to the manga, he became a chimera ant and had all his human memories intact. He escaped while the queen was dying and supposedly went to Meteor City to start his empire again (according to the manga). I think they might have him return in the future as a super villain or something, because in ep 79 or 80 it showed his back story and his thoughts on humans. He wanted to bring evil in his human form, so why not in his chimera ant form?
Gyro was not re-born as the Chimera Ant King, Meruem. Gyro was killed and eaten by the Queen, turned into a Chimera. But he re-gained every single one of his memories and fled to Meteor City to rebuild his Empire. It says so in the manga and on Gyro's Wiki page.
Gyro was killed by the chymera ants why i say this is because when the ants invaded gyro was seen seated in his chair and in the next scene the chimera an't who looks like a centuar said "Gyro huh..wish i could know more about him..well no use dwelling in it now what's fine is done "
In order words gyro was killed and eaten by the queen and born as the king 'meruem' and that explains why meruem was do evil from the start because when the narrator was explaining gyro's past he said gyro is evil hence the king' s behaviour Gyro would have without a doubt continue to be evil if it weren't for komugi and that's why he did not even bother to take out the five million humans with him to hell
Gyro 'muruem' was killed by the poison by netero and died along with his love interest kumogi
So in conclusion gyro is the king of the chymera ants mureum