You dont even need a separate partition, just delete the non-home directories and reinstall. pacstrap might even do that for you 🤔 it has been a while since i last needed to reinstall. And most of the time you dont even need a full reinstall, Arch is trivial to fix most things from a live cd by partially following the install process - most often get a chroot and start reinstalling select packages/configs in some of the worst case scenarios.