Just today I used Kohl's Cash from April. The cashier never blinked. She scanned it and I saw a popup on her screen that said that it had expired, and then she had to respond to that pop up and then enter a transaction discount. That is how it appears on the receipt: "$ TRANSACTION DISCOUNT 40.00-"
However, be sure you definitely will want to keep what you are purchasing because since it is considered a discount off the purchase price there is no way to get that money back,even as a store credit. So in my case I spent $40.78 and got a $40.00 "discount". If I were make a return I would be entitled to 78 cents, and yes I know that from experience also. But, hey, they are letting you used the expired "cash" so...so be it.
From the previous post, each store must have it's own policy. The way I found out the first time I used it was to simply go back to customer service, presented the expired "cash" and asked if it was possible to use it. Again, the rep never blinked--she had heard it 100 times, and she did mention to me at that time that once I used it the sale would be final.