A dead man's switch could be activated in the case that your friend doesn't log in to his computer and enters a password or code every 10 days for example. The moment he stops doing that someone else can receive access to his accounts.
Another possibility is that your friend creates emails for the future. The site https://www.futureme.org/ allows you to write an email that will be sent at a specific date in the future. There is a similar service here - http://whensend.com/