You could create a new role, set it to prevent all student's capabilities, and assign this role to the drop-outs. If(!) my guess is correct, the users might still be treated as enrolled in the course, but they wouldn't be able to do anything in it.
A quick idea, not sure if this will work, so please test it before using it on a real student 
You could create a new role, set it to prevent all student's capabilities, and assign this role to the drop-outs. If(!) my guess is correct, the users might still be treated as enrolled in the course, but they wouldn't be able to do anything in it.
You could create a new role, set it to prevent all student's capabilities, and assign this role to the drop-outs. If(!) my guess is correct, the users might still be treated as enrolled in the course, but they wouldn't be able to do anything in it.