If he heard this from heaven, I bet he'd be seriously angry
If he was listening to us from heaven, he would probably be really mad
He would be seriously angry if he had heard this from heaven
天国にいる彼がこの話を聞いてたら真顔で怒るだろうね と言いたい場合はたくさん言い方があると思いますが、３つを挙げてみました。
If he heard this from heaven, I bet he'd be seriously angry
If he was listening to us from heaven, he would probably be really mad
He would be seriously mad if he heard us from heaven
個人的には回答３が短くて伝わりやすいと思います。
ご利用いただいきありがとうございます。
またの質問をお待ちしております！
カナダ 
