就跑了

then ran off

→ 就
phrase Rare #21,716
then ran off 就 links the preceding event or condition to the immediate action; 跑了 means someone ran off or left by running.
CH: 他听见声音就跑了。
EN: He ran off as soon as he heard the sound.

结果他们留下就跑了追都追不到

In the end, they left and ran off, and we couldn’t even catch up with them.

— I Am What I Am (2021)

一开门他就跑了

As soon as I opened the door, he ran away.

— 阳光灿烂的日子 (1994)

知道孩子有病就跑了

They ran off as soon as they found out the child was sick.

— Dying to Survive (2018)

我呢我把狗留在那里就跑了

As for me, I left the dog there and ran away.

— 预言者 (2009)

抛下我就跑了

You just left me behind and ran off.

— 分手的决心 (2022)

但是要等我们拍完了再提醒他不然这个混蛋肯定一听说就跑了

But we have to wait until we're done filming before reminding him, or that bastard will definitely run off as soon as he hears about it.

— 雨水危机 (2011)