I wonder what would have happened if I didn't have that talk with him.
I can't imagine what would have happened if we didn't talk that other day.
(1) I wonder what would have happened if I didn't have that talk with him
'i wonder' =「疑問に思う」「気になる」
'what would have happened' =「どうなっていたのだろうか」
'if I didn't ~' =「もしも〜をしていなかったら」
'have a talk' = 「話し合いをする」
「もしもあの話し合いをしていなかったらどうなっていたのだろうか」というニュアンスの訳出です。
(2) I can't imagine what would have happened if we didn't talk that other day
'i can't imagine' = 「想像できない」
'talk' = 「話す」
'the other day' = 「あの日」
直訳すると「もしもあの日話をしていなかったらどうなっていたかが想像できない」です。