How to unpublish nodes 50 days after they are created by using the Rules module?
Have you looked into Rules Scheduler? The process is similar in that you create your rule, create a component that unpublished content, then use Rules Scheduler in the original rule as the action to run the component 50 days after "date published". Here is a video of scheduling nodes to be published after X time that you can follow: http://www.youtube.com/watch?v=OgRKLXRbPX8 .