vrms is the tool for the job in Debian. It goes through all your packages and
checks where they came from; if they came from a "contrib", "non-free",
"restricted", or "multiverse" section, it lists them appropriately.
To my limited understanding, a repo is nothing but a server.
Unmarking it should only remove access to it, not to what you installed from
it.
You'll need to remove the non-free software installed.
vrms would be useful for that purpose.
https://packages.debian.org/jessie/vrms
In debian 8 64bit if you mark non free repositories and install non free
software. If you unmark the non free repositories does the system get free
software? Or you have to uninstall non free software one by one? Thank you.
https://screenshots.debian.net/package/software-properties-gtk
