You have lifetime access to your course content. After your course ends, just log in as usual at forksoverknives.rouxbe.com/login and click on the photo of your course tile to go to your Course Home page. Click on any task to go directly to it.
If you are taking the Essentials course: There are no deadlines for optional assignments, and no end date for your course.
If you're taking the Ultimate course: After you graduate or your 90 days expire (whichever comes first), the only areas locked will be the quizzes, instructor-graded assignments, and the Question & Support function. Other than that, you will still have all the lessons, recipes, etc. to review at your leisure.