Gentoo used to include a static busybox binary for recovery purposes, but it was removed from the system set years ago. Now you are expected to use the initramf

Gentoo used to include a static busybox binary for recovery purposes, but it was removed from the system set years ago. Now you are expected to use the initramfs for recovery and can install bust box yourself if you are concerned. In fairness, this particular issue would be made worse by rebooting since the unlinked anonymous library files would be garbage collected, which is bad unless you have a filesystem that has snapshots like ZFS and had used them prior to this. The article author did not try to recover libraries from the anonymous files, which is probably good considering that only a subset would have been in use and thus only that subset would be recoverable from the anonymous files (unless there are filesystem snapshots).