There is nothing worth of freaking out in your situation. Your files shouldn't have been impacted at all.

Boot from LiveUSB and reinstall the packages you were updating, maybe reinstall grub too.

There are tons of guides for this in the Internet, like this one: https://www.jeremymorgan.com/tutorials/linux/how-to-reinstall-boot-loader-arch-linux/

Edit: since you probably use systemd-boot, as I can see from your post, obviously the grub part of my comment shouldn't be done. Replace those parts with systemd-boot reinstallation. Even better if pacman will update it, because there's probably some hook already to do things manually and you won't have to touch systemd-boot at all