Strange as it may seem, if the SC is bounced by the paying bank to you as depositary bank, there's nothing other than precedent and perhaps state law (doubtful) or your own deposit contract that requires you to return the item to your depositor. You do have to notify your customer of the dishonor of the check (Reg CC and UCC requirements) within a midnight deadline. That notice need not be in hard copy written form.
And if you determine that you need/want to return the item, you can return a copy of the SC rather than the SC itself.
John S Burnett