I think Johnny is ultimately just Johnny. His growth throughout the game is coming to terms with the fact that he lost the fight against the corps and that the ends never really justified the means when he hurt the people close to him. He has to accept that he was always just a scared kid in an unfamiliar country desperately pretending to be hard enough to survive.

So...I think you can trust him to fuck shit up and fight the corps basically as soon as he calms down from realizing he is still alive. If it carried even a slight chance of success, I think he'd happily walk into Arasaka tower on a suicide run the minute you see him in the diner.

I don't think he'd hand your body back until you're chooms though, which is really cemented in the grave scene.