I'm worried about that too, but you can deal with it by making the system that automates your backups also test your memory of the password (while still creatin

I'm worried about that too, but you can deal with it by making the system that automates your backups also test your memory of the password (while still creating a non-interactive backup even if you ignore the prompt). Alternatively, reuse a password that you regularly use offline, like a disk encryption or SSH passphrase.