Fail-safe remote API operations for managing customers and billing
Do you have access to the customer API? If so, I think the deletion of the Paypal account should be handled by it.

If you do not have access to it, it seems the most important call is the Paypal one, so you should first make sure that one succeeds. Once it does, you can delete the customer account. But no matter how you delete it, there will be some time, even if only a few seconds, when the customer account will be without a Paypal account. The customer API needs to handle this situation gracefully.

To make sure the customer account gets eventually deleted, I would add this account to some table and have a cron job process it every X seconds. The cron job should delete all the account in that table. It means that if deletion fails, it will try again a few seconds later, so it's safe to assume the account will eventually get deleted.