TL;DR
GNOME Software removed most packages and I didn't create a snapshot of my /var directory and now pacman thinks most packages aren't installed.

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So... I managed to pull the Linus and nuke my DE by uninstalling "Avahi Zeroconf Browser" which supposedly uninstalled basically everything. (Yes, I sadly did it using GNOME software and everything was just gone without any message after typing password.)

Because I though, that i am something going to need it I setup snapper and snap-pac to make snapshots on every package install, but due to my (mis)configuration It didn't create a snapshot from /var/lib/pacman directory. So basically I got everything installed, but pacman thinks nothing is installed.

Is there some way to fix this, or am I left with doing a complete reinstall?