要不然

He reminded me of what I should otherwise have forgotten.

亏他提醒我, 不然我就忘了。

Don’t go too far afield or you’ll get lost.

别走得太远, 不然你会迷路的。

Make haste, or (else) you'll be late.

快, 不然就来不及了。

Make haste, or we shall miss the train.

快, 不然我就赶不了。

Prices seem to have stopped rising in the shops, or is that just wishful thinking on my part?

商店里东西的价格好像不再涨了，不然就是我的廂情愿？