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.
The subscription can be renewed manually as well, again through My Chaos.
Please bear in mind that the subscription can only be renewed before it reaches its final expiration date, once it 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.