Wallace would never have gotten the nomination. If he did: I think we would have seen a left-wing 3rd candidacy, gaining some support, but Reagan would have won by a significant margin.
✓ Former Governor Ronald Reagan (R-CA)/Senator Richard Schweiker (R-PA): 425 EVs.; 48.1%
Governor George Wallace (D-AL)/Representative Mo Udall (D-AZ): 113 EVs.; 42.2%
Former Senator Eugene McCarthy (I-MN)/Former Represenative Pete McClosky (I-CA): 0 EVs.; 6.7%
Reagan would win Maryland and Delaware in this scenario. They were both fairly close in real life, Wallace was much less palatable than Carter, and Schweiker was a moderate from the Philly suburbs, so him being on the ticket would give Reagan the boost he needed.