You will want to develop a procedure for staff on how you want to handle trials.
If a trial becomes an enrolled student, delete the Future Drop date from the class Enroll List tab and change the Enroll Type to Trial-Enrolled. This can also be done from the student's Classes tab.
If the student doesn't enroll, staff should make sure a future drop is in place; and if not, drop the student from the class.
If no change is made, and the student remains as Enroll Type = Trial, it's possible that the student will be excluded from your tuition posting. This could happen if you always set Enroll Type: Trial: Post Tuition Fee? to No, Skip when using Transactions > Post Tuition Fees.