Can one recover from an accidental rm -rf of system directories by copying those files back in from a backup?

Well I’ve joined the “accidentally trashing your system with rm -rf” club! Luckily I didn’t delete my home directory with all the things I care about, but I did delete /boot and /usr, and maybe /var (long story, boils down to me trying to delete non-system directories named those but reflexively adding the slash in front...