It is highly unlikely that this would happen to you, and this is why I am sure this bug happened to me (plus regional upgrade (RU) certs are still rather new-ish at Delta).
First some quick facts to be aware of about these certs. As you can see by the T&C you CAN transfer or assign this cert to someone else traveling with you. It says on the same reservation, but we also know in practice if this someone is on the EXACT SAME flights and you have “linked” your reservations then they can also assign the cert to them as well.
And, if you have the latter situation, this is where the bug can occur. If, for whatever reason the flight is canceled and Delta has to re-deposit the cert back into your account, the one that was used on the linked reservation will end up going back into their account instead of yours (kinda funny if they are not a PM or DM).
Another interesting bug is the cert seems to be reissued as a new cert with a new expiration date. So, my expiration date for the cert was reset from the date I redeemed the cert to this new date when the flight was cancelled, giving me a year from the cancellation date to spend the cert.
As most of us know the Delta RU certs are having some issues. There are times they are NOT properly applied and you miss an upgrade. There are times you request only for it to be applied to the entire trip (one-way) over multiple flights or not at all and they pull the cert for just one short segment. I know, very frustrating; but after all we are talking Delta IT here who has to hide the award charts to make sure we can not see pricing issues. 😉
Anyway, this is just one I wanted to make you aware of as if you have this case be sure you let the reps knows about it, before you hang up, or your partner is likely to end up with one of your RU certs! – René