Programms (binaries or scripts) will be not killed during logout, if the
realated programms was started from an "forEver-script"

Autostart-file in XFCE: ~/.config/autostart/autorun.xxx.desktop 

[Desktop Entry]
Comment[de_DE]=
Comment=
Exec=/home/<user>/forEver.sh
GenericName[de_DE]=
GenericName=
Icon=system-run
MimeType=
Name[de_DE]=
Name=
Path=
StartupNotify=true
Terminal=false
TerminalOptions=
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=
X-KDE-SubstituteUID=false
X-KDE-Username=

####

File forEver.sh : 

#!/bin/bash
while true 
do
<executable binary or script> 
done

##########

After logout from XFCE this <executable binary or script>  is still running.
For test: i used xclock as <executable binary or script>