I asked them what the process would be if myself or one of these former employees had died - and was given the run-around. Every single thing they told me to do did not work and just exposed another exception.
There are multiple contacts in amazon -- Billing, Operations, and Security. If you have access to the Billing email you should use that for contacting them.
Otherwise it looks like a credit card dispute might trigger a cancellation or similar but I don't know for sure.
If the addresses are on a domain that you do not control, well, that’s a lesson learned for you I think. In this case, you’ll need to continue working with support to explore what can be done.
Ultimately, we were able to close the account with the consultants' cooperation.
I get your point that it's wise to remove consultants promptly after their contract concludes, and I agree. However, this doesn't take away from the fact that AWS's account closing policies appear to be less than user-friendly.
You'll probably be fine.