This has been discussed on several threads, and others may disagree, but the Terms and Conditions indicate that you must be a card holder at the time of travel:

"1. You are only eligible to receive a Redemption Voucher for a companion if you are a member of the BA Executive Club and are the main account holder within a BA/Chase Credit Card account (a “Member”)."
"17. Members must remain eligible for this promotion at the time of travel. BA and Chase reserve the right to withdraw any Redemption Voucher in the event that the Member is in breach of the terms of the BA/Chase Credit Card or the BA Executive Club Terms and Conditions."

Thus, only cardholders are eligible to receive a voucher, and you must remain eligible at time of travel. (It is unclear whether BA and Chase are enforcing these provisions.)

You pays your money, you takes your chances.