Not necessaryly are silver strikes, or any casino money type items(chips, tokens, etc.) ALWAYS redeemable. Most all gaming boards, commissions, or casino governing enties in this country. Require that a NOTICE OF REDEMPTION. Be posted and advertised by a casino closing or a casino that wants to not redeem something anymore. This notice of redemption, will state that after a certain date. A minimum time limit is set by the regulating enity. Usually at least several months or more. The item or items listed in the Notice of Redemption. Will not be redeemed by the casino posting the Notice of Redeemption anymore. If the listed item(s) are not redeemed by the posted date, the person is "stuck with it or them", so to speak. Unless they can find someone else who wants it or them.

A fairly recient example was the fairly fast & unexpected closing of the WESTWARD HO CASINO. The Westward Ho Casino owners. Made a agreement with the RIVERIA CASINO across the street. To redeem their casino money type items, for them. As they did not have enough time to do the requireed redemption notice time, before they closed down.
I hope this answers your question.
Dan