Should I add a person who left my group to my evolved paper?
It is good to minimize the number of academic enemies you have. Purely as a strategic move you might just want to ask them unless it seriously offends you. That seems better than making an assumption one way or another. 

How much contribution is enough depends on a lot of things, including field and place, of course. But helping with "high level" direction doesn't sound like it is trivial. 

Of course, in asking if they would like to be on the paper you could say that the "paper has evolved quite a lot since you were last involved". 

Pick your fights for when they really matter, I think. Especially as a post-doc who wants to move up.