if so
If (something) happens. The phrase is typically used at the beginning of a sentence. I think it's supposed to rain tomorrow. If so, the game will have to be postponed. A: "I'm worried that Sharon ruined the surprise." B: "Oh well. If so, we'll just have to regroup and come up with something else."
if so
if that is [the case]; if that is so. She might be late. If so, we will eat without her. She is supposed to be all right. If so, we have nothing to worry about.