For my ILCs, I close the enrollment two weeks before the class starts. I just had a user that wanted to cancel the session, but the Cancel Session button was unavailable because the course enrollment window was closed. I changed the End Enrollment dates, and the Cancel Session button was there.
I think it is important for users to be able to cancel a session themselves after the enrollment closes so that an Admin does not have to do it.
We might be able to solve this with a "Cancel By" date the administrator can specify. It is really a solution for https://ideas.absorblms.com/ideas/LMS-I-398 but could apply here as well.