Barry Goldwater ran as a candidate of the far right in 1964, and was slaughtered in the general election. The great liberal victory made it possible to pass a substantial amount of the Great Society legislation.
If Ted Cruz is the nominee, he will be the most right-wing GOP candidate in a general election since Goldwater. Would the result be the same? I am confident he would lose, but the impact on Congress would be more limited, because, due to gerrymandering and natural forms of segregration, there are relatively few GOP House seats that would be vulnerable even in a landslide.