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Given these options we've chosen 4 as the safest, most cost-effective path forward and have stared a runbook for it. We have also tried to catalog all of the places where the table is currently touched in the platform.
For any solution we will probably have to drop the foreign key from courseware_studentmodulehistory, according to the prod database and grepping through code there are no other FKs to / from this table, which seems suspicious.