In the phrase:
why would you choose to use 立ち去る rather than just 去る? Is there a possible ambiguity from using just 去る? Does it have a different nuance?
立ち去る and 去る are probably interchangeable in your case, but when you describe something that can happen everyday, 立ち去る would sound a bit safer.
According to the dictionary, 立ち去る means to actually get up and leave a place:
So the meaning is slightly different than just 去る (to leave).