Board Thread:Episode Discussion Board/@comment-112155-20151020210425/@comment-24939040-20151021083724

Another reason why Garner probably isn't dead: Coulson wouldn't let a valuable asset out in the world without protection. Just like Bobbi was Jemma's backup in Hydra, either Garner has a bodyguard we didn't see OR Garner has a high-tech defense. (Or, as somebody said above, he knows self-defense.  He used to work for SHIELD, after all.)

Oh, and a press release for 3x06 lists him in the cast ...