Yes Kohl's cash can be used after it expires but you must use the Kohl's cash in stores within 10 days of the expiration date.
After 10 days past expiration date on the Kohl's cash it will likely not be honored in the store however sometimes it might.
You cannot use expired Kohl's cash online though but only in stores.
The Kohl's Store will honor the Kohl's cash expired coupons 10 days past the expiration date.
So there's no need to throw them out because the store will usually honor them for 10 days past the expiration date.