I think the value is going to be depressed. Right after his death would have been the ideal time to sell, imo. However, it depends on collectors, and what they are willing to pay, and what books they might need to finish their series.

Also, going with any second hand book store, or middleman you're looking at them offering you a price with them turning a profit in mind. A book may be valued at $100 a pop, but if they sell for that, you may be lucky to get $50

And you have to look at the books themselves and the popularity of the series at them time. A first edition signed The Eye of the World is going to be worth more then a signed Knife of Dreams.

All in all I'd hold onto them. They may be worth a lot more post A Memory of Light, and Encyclopedia WoT.