For AWS accounts that are NOT part of the Cornell Enterprise Org, when closing, one faces the same issues as terminating resources then closing. However, without a 3rd party tool like CloudCheckr I can be a rather manual process.
Below are some docs that can assist with walking thru the process.
How do I check for active resources that I no longer need on my AWS account?
https://aws.amazon.com/premiumsupport/knowledge-center/check-for-active-resources/
How do I terminate active resources that I no longer need on my AWS account?
https://aws.amazon.com/premiumsupport/knowledge-center/terminate-resources-account-closure/