Nixon either dies during the trial (he was reportedly a physical and mental wreck in the immediate aftermath of his Presidency, and his phlebitis and pulmonary embolism weren't helping), or the trial is dragged out through the Bicentennial and election, with every dirty deal and morally questionably thing done by the Nixon, Eisenhower, and other administrations bought to the limelight for the American Public. There would ultimetly by no national healing, and Ford would be seen as a traitor throwing Nixon under the bus by detractors, an image that wouldn't be helped if Nixon dies.
If Nixon lives to 1976, you will have Ford overshadowed by the trial- if he dies, you have Ford overshadowed by Nixon's death. Reelection may be harder under these circumstances.