Hi @Lynn9,
There are different statuses in a Canvas course ("active", "inactive", "deleted", and "concluded").
Canvas Enrollment Status Comparison - Instructure Community - 387055
I do not have a lot of experience with the "concluded" status but if the student that withdrew from (or dropped) the course has a status of "deleted", it is not possible for an instructor to view that student's grades or activity in the course.
I would recommend that you check with your Canvas team to find out what the Canvas enrollment status is for that student and find out if it is possible for it to be changed (either permanently or temporarily) so that it the student is "inactive" in the course.
-Doug