Can you be considered a former VP candidate if the guy that selected you never became the nominee? Unchartered territory here
It is charted, since Reagan in '76 names Richard Schweiker his VP choice before the convention, and it didn't work for RR either. When Reagan won in 1980 with GHWB, Schweiker became his HHS Secretary. He isn't thought of as a nominated VP candidate, which is what will happen to Fiorina, barring a massive shift in the present trend.
P.S. Schweiker was a WWII vet (electronics technician in the USN, I remember since my father was a civilian ET at the Philly base and in Yokosuka), and stayed married to the same woman until he died last year.