(This is different from Blackboard and presents some opportunities for considering how students could benefit from continuing to access content in previous classes. At the same time, you might want to consider what elements of your course you wouldn't want to remain available to the previous students. Don't worry - by default quizzes and tests cannot be accessed by students in Past Courses.)
For faculty, we have some flexibility about how long concluded courses remain on the Dashboard.
Once courses are moved to the Past Courses area of Canvas, faculty may no longer change grades or edit the course, but they may continue to access it as much as they like and even bookmark it for quick viewing. This will reduce your Dashboard clutter as well. Keep in mind, when building new courses, you may always copy from any concluded course, whether it is in the Dashboard or in the Past Courses area.
Should a student need to finish an Incomplete, this is a special process and it doesn't matter whether the original course is in the teacher's Dashboard or Past Courses area. Either way, the revived course will become visible on the Dashboard of the teacher and only the student finishing the Incomplete.