How to remove systemd from a Debian jessie/sid installation
From Without Systemd
First install the SysV init packages
# apt-get install sysvinit-core sysvinit sysvinit-utils
Then reboot your machine and remove all of the systemd packages. BE AWARE that the following command removes packages that depend on systemd itself or things like libpam-systemd!
# apt-get remove --purge --auto-remove systemd
Prevent apt from installing systemd packages in the future.
# echo -e 'Package: systemd\nPin: origin ""\nPin-Priority: -1' > /etc/apt/preferences.d/systemd