Add opacity to the body tag and decrement it daily or weekly until the site completely fades away. Set a start date, type(DAILY or WEEKLY) and provide the number of days or weeks you offer them until the website has fully disappeared.
// Change the `type`, `date` and `count` variable to match your preferences
var date = '2020-09-14'; // the date to start
var count = 30; // days or weeks after which the contents will disappears completely
var type = 'DAILY'; // how often to decrease the opacity: 'DAILY' or 'WEEKLY'
Just load the unpaid.js file in <head>