Hello!
Hope you love the macOS and will not return but if so, it does look like you would either need to return the Beats with the Mac or have the value of them deducted from your refund.
"PROCEDURES RELATED TO PRODUCT RETURNS AND EXCHANGES: Returns and exchanges are subject to the policy of the Qualifying Location where the purchase was made. If an Eligible Product is returned, or is exchanged for an ineligible product, the Promotion Product must also be returned in its original packaging or the Promotion Savings will be deducted from the amount of the return or exchange, as applicable, and any remaining difference will be charged to the Qualified Purchaser."
This promotion is for Education purchases. Terms and Conditions shown here: EN_US_BTS_FY19_TandCs.pdf