If you updated the same SCORM content file, without renaming the course/file most systems handle the minor changes gracefully and do not orphan the student's who have completed the course. Students that was mid-course, will have to start over.
Normally, if it is a rather large course, I would send out a notification to encourage students to complete or not start the course by a specified date. Informing them, that they run the risk of loosing their course progress and then make the update after the provided date. 6000 learners on a 90 minutes, we only lost 3 student's progress - and they were informed before the update.
However, if you content had a major change, I would think you would want all students to "retake" the new, revised course.
