You can buy credits using a bank transfer [1]. You can also set E-Mail alerts in case your monthly invoice is higher then expected (more traffic etc.) [2]. However, there is no auto-delete as far as I can tell.
[1] https://docs.hetzner.com/accounts-panel/accounts/payment-faq... [2] https://docs.hetzner.com/cloud/billing/faq/#how-do-i-keep-my...