There was little chance that Nixon would have picked Reagan as his running mate in 1968.
Reagan was considered to be an affable Goldwater conservative by the Republican establishment, at a time when Goldwater-style conservativism had been discredited by the landslide loss of 1964. Nixon felt that, given his anti-communist credentials from the late 1940s and 1950s, that he was conservative enough and that conservative Republicans really had nowhere else to go. Independent George Wallace was a populist tainted by segregation/racism who couldn't win, and he was something of a big spender as the Democratic governor of Alabama. So there was little fear that conservative Republicans would vote for Wallace. Plus, Nixon was from California as well, so he didn't feel that he needed Reagan to help him win that state.
As in 1960, Nixon in 1968 was looking to pick an Eastern Establishment Republican or someone acceptable to that wing of the party, which Reagan was not. Gov. Spiro "Ted" Agnew of Maryland was associated with the Rockfeller Eastern Establishment wing of the party, but he was also a tough law-and-order governor, which is why Nixon picked him.