YOU SAID:

when the cat is away the mouse will play

INTO JAPANESE

猫がいなくなるとマウスは遊ぶ

BACK INTO ENGLISH

When cats are gone, the mouse plays

INTO JAPANESE

猫が消えたとき、マウスは遊ぶ

BACK INTO ENGLISH

When the cat disappears, the mouse plays

INTO JAPANESE

猫が消えると、マウスが遊ぶ

BACK INTO ENGLISH

When the cat disappears, the mouse plays