彼が来ようが来まいが

whether he comes or not

→ 彼
phrase Rare #40,241
whether he comes or not A formal or literary construction meaning that the result is the same regardless of whether someone does something. 来よう is the volitional form of 来る, and 来まい means “will not come” or “does not intend to come.”
JA: 彼が来ようが来まいが、私は行く。
EN: Whether he comes or not, I will go.

彼が来ようが来まいが重要ではない

It doesn’t matter whether he comes or not.

彼が来ようが来まいが私は行く

Whether he comes or not, I’m going.

彼が来ようが来まいが結果は同じだろう

Whether he comes or not, the result will probably be the same.