I'm trying to figure out what こうなれば/こうなりゃ means in the sentence
なれば ＝ それだから。したがって。
The Google fish says こうなれば ＝ "in this way," but it seems like it should be translated as "thus," or more literally, "if it has become so".
They've managed to call their friends! Thus, I will continue to smash them one by one (beginning now until some future point in time).
Is こうなれば interchangeable with こうなったら?
仲間を呼ばれた！こうなりゃ一匹ずつ潰していくまでだ。
Here the こうなりゃ (contracted way of saying こうなれば) means "Now that it has come to this" "Now that things have come to this", and can be rephrased as 「こうなったら」「こうなったからには」 or 「こうなった以上は」.
(beginning now until some future point in time)
The 「Vまでだ」 here is not "until" but "only" "just" "and nothing more" or "all I have to do is~~", close to 「Vまでのことだ」「Vだけのことだ」.
"Now that it's come to this, all I've got to do is smash them one by one."
Yes, こうなれば is interchangeable with こうなったら. They can mean about both "future events" and "what has happened".
On its own it means "In that case", or "if that happens", or something along those lines.
Your quote seems incomplete or incoherent to me.
