Clint or a Winchester brother is pretty much alone at an outpost or garage in the middle of the desert post-apocalypse (not neccesarily the bomb, but more societal breakdown). A man dressed in a suit and tie comes walking out of the desert. Turns out Phil is either the last SHIELD android (is that the term they use?) or the last rogue/friendly android. Tony helps repair him (hot desert sand can be rough on the system) and he helps protect them from SHIELD. I'm not clear whether it was crossed with SPN or not.
Goddess, that was vague, but I'm been going over this in my head for a couple days and that's the best I got. It was written before Ultron, Vision, or the twins.