Now Reagan -Rockefeller '76 is a fascinating what if?
However, I think it is too close to the "WI Reagan gets elected in 1976" posts that have appeared on this site.
The Reagan -Rockefeller ticket would probably win. Its an upgrade on charisma on Ford -Dole, and the OTL 1976 election was one of those close ones where just about anything changes the result.
If Carter wins anyway, Rockefeller still dies in 1978 and Reagan is still the Republican front runner in 1980. Defeating a sitting Presidents in the primaries would enhance his reputation, even if followed by a close general election defeat. IOTL, Ford considered running in 1980 after his close defeat. So not much really happens.
If Reagan wins and Rockefeller stays as VP, you really just get a 1977-81 Reagan presidency, and this has been done, especially as if he had won the Republican primaries he almost certainly would have picked a liberal such as Schweiker (sp?). The Vice President doesn't have alot of influence on the day to day operations of the executive branch, in fact this was increased quite a bit when Mondale held the office, which IITL doesn't happen. And Rockefeller might still die in 1978.