If you are in a big hurry to get back to CSR after EPCOT closes, walk (via the IG entrance) to either the BC or BW. Then grab a cab - it's ll cost you $10 - $15, including tip. That's the absolute quickest and least congested way to get back to CSR (or any non-EPCOT resort) after IllumiNations.
If you are not in a hurry and just want to avoid crowds, find a bench somewhere in World Showcase and people watch for 30 -45 minutes or so. It's even nicer if you have a drink to sip while you wait. When the crowds decrease, walk out through the main entrance and catch the CSR bus. You won't find much of a line (if any) for the bus so you won't have to stand, and it's nice to walk out without the crowds. And you won't get back much sooner than if you rushed out with everyone else - most just spent the time waiting in line at the bus stop and/or wishing they could sit instead of stand.
I think rushing out right after IllumiNations is way overrated - I won't ever understand while people leave events early just to "beat the traffic". Seems like a common habit here in Minnesota - they leave early from Orchestra concerts, all the ball games, and even the live theater plays that cost over $100 a ticket! Don't know why they don't want to see the ending, LOL!
Best wishes -