I was under the impression he was getting up there in years. I also think the reps will want to go with a "nice guy" . After the past 8 years of hate by the left, chances are the GOP will look for a squishy moderate to try to please everyone.
Just my speculation, I don't have any hard info.
Cheney has health issues, I am sure even if he his healthy, he would want some years in retirement, and might want to step down to enjoy the later years in his life.
Combine this with the potential of helping the party by giving them a NAME as VP for a couple years, I think it is possible.
Cheney cannot win the Presidency and do you really think he wants to be VP for 12 more years? I just don't see it.