I'm not horribly against the idea of dropping the FK, but maybe I'm not fully understanding the advantage of doing so. How does deleting the parent records first improve performance?
It's not guaranteed, but it might.
Since the date column that determines deletion-eligibility is in the parent table, to start the deletes from the child table requires joining from the child to the parent.
If that join is a lot of overhead and/or very slow and/or causes delays to other tasks, then starting the delete from the parent table and avoiding the join can speed things up.
If that join is not particularly performance-harming, then do the join, delete from the child first, and use the OUTPUT results from the child delete to delete the associated parents.
I didn't mean to overstate it. I'm not gung-ho on disabling/removing fk constraints, but there are sometimes situations where it can really speed up delete processing.
SQL DBA,SQL Server MVP(07, 08, 09) Prosecutor James Blackburn, in closing argument in the Fatal Vision murders trial: "If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them."