The Chaos V-Ray is a term (monthly/annual/3-year) subscription license so once it reaches its expiration date, you need to renew the subscription to continue working with the products.
All term licenses come with an auto-renewal option enabled which means that once the subscription reaches its expiration date it will get automatically renewed for another billing cycle. This option can be disabled/enabled at any time through My Chaos.
Once the license expires and you want to use the product again, you will have to make a new purchase for a new subscription.
Chaos Cloud credits included in the Chaos V-Ray Premium/Enterprise license are also term-based and will expire together with the whole license.