What is the deadline for cashing last year's reward bonus?

I thought those never expired, call the store directly too make sure tho

If you're talking about your Costco 2% rewards check that check never expires if you're referring to the Visa that one does expire for cashing out but you can always use it for Costco merchandise even after the expiration date

Not sure you would have to call your local Costco to find that answer.