A power cut during update-initramfs may leave the system in an unbootable state as the old initrd.img is
overwritten, but the new initrd.img is not yet completed. (This happened to me when my laptop battery ran empty.)
A simple fix would be to create the new initrd.img as a temporary file and move it to replace the old initrd.img
only after image creation has been finished. That way, the chance to have an unbootable system after a power cut
would be significantly lower, restricted to situations in which the old initrd.img doesn't work anymore.
A better fix would be to always keep a copy of the old vmlinuz/initrd.img pair
or ramdisk including vmlinuz.
This would solve lot of problems of this kind, and always keep one or more
fallback to older kernels.