@Cari
"it becomes a a lot of work on us if every teacher has to reply on us for this"
What do you mean 'reply'?
Assuming there is a calendar ... with course end dates ... and new academic session begins.
You could inform your teachers that one day after course end dates, you will make a run of all course backups - moosh - looping shell script (course id's) that saves backups to a directory on server - or remote storage.
You could then give teachers control on resets ... or after the backups have been completed, make a run of moosh looping shell script (course id's) that reset's courses.
If there are many courses, could break apart the looping - 1st session course ID's 2-200, 2nd session course ID's 201-400, wash, rinse, repeat - until finished.
For duration of such, recyclebin set to retain 1 second and if a space crunch, one could include in scripts a command to delete contents of moodledata/trashdir/ to re-coup free space. After resets, return settings of recyclebin to something sane.
So issue is solvable ... just have to corrdinate a plan with teachers!
'SoS', Ken