This may be weird but it really depends on the setting and when I ran into him.
If I was out in public and just happen to somehow cross paths with him I'd probably just be like.. "hey Em" and be on my way.
If it were not in public and no one around.. basically if he wasn't too busy, I would just talk to him. Ask him how he's doing. Small talk. Nothing serious.
..But it were to actually come down to it and happen I really couldn't say for certain. I think most would be the same way too.