It is worth whatever you can get someone to pay for it. As we know location, condition, miles, market, color, options, transmission all play into it. KBB for my very clean defect free 99,000* mile 2010 JSW as if today is:
$10,201 to $12,720 Trade In
$10,833-13,521 Private Sale
The interesting thing the buyback is based on KBB at a date just before diesel-gate news broke, was approx $11,000. So I get about $16K I recall (been a while since I looked it up). You can see KBB is about the same or slightly higher today.
I'm planning to have it fixed (pocket $5,000) and keep it. If I decide to sell it I will do better than selling it to VW (if I can get someone to buy it for $11K). My engine is from a 2013 and has only 46,000 miles. So I hate to sell it. I did just buy a second car a Nissan LEAF... It's a great car but not a stand alone do all car like the VW is. Plus the VW has a Westfalia hitch and VW CAN trailer wiring.