As promised, Josh Charles dropped in to visit David Letterman on The Late Show to explain just what in the holy hell went down on Sunday's episode.
OK spoilers, obviously (but if you're clicking on this and you're way behind in your Good Wife viewing you should only be mad at yourself if the ending gets ruined for you, OK?).
He didn't really go into anything we didn't know already (Charles left the show because he wanted to move on; they planned his death for a long time, etc. etc.) Of course, he talked about fan reaction—keep in mind Charles has a pretty active and sort of awesome Twitter account. So he's not one of these celebrities that goes around believing they live on a beautiful pink cloud made of fairy dust where no one ever has anything bad to say about anything ever.
TL/DR he knows you are all going NUTS about this and he appreciates the enthusiasm for the character but you know, he's moving on. Just like your boyfriend in college who moved to St. Louis on a whim, you can't convince him to stay, OK? He already shipped most of his stuff to his aunt's place and his plane leaves tomorrow. Yes, he didn't tell you about it, but you shouldn't take that to mean anything other than he just really, really wanted to move to St. Louis and work at that Petco by his aunt's house. That's where his soul is taking him. These things happen. Let it go.