Rob K mentions in his answer, in your example A has already defined the context, so "it" is perfectly clear.

However, it is not uncommon to say a pronoun without context, but it is awkward since the listener would not know the reference. You would have to add some further explanation what you mean.

A. I'm sorry, it's completely sold out
B. What are you referring to?
A. The game. It's completely sold out.

I don't think this is unique to English, since it's more about the general quirks of pronouns or any ambiguous part of speech.

As Rob K mentions in his answer: In your example A has already defined the context, so "it" is perfectly clear.

However, it is not uncommon to say a pronoun without context, but it is awkward since the listener would not know the reference. You would have to add some further explanation what you mean.

A. I'm sorry, it's completely sold out
B. What are you referring to?
A. The game. It's completely sold out.

I don't think this is unique to English, since it's more about the general quirks of pronouns or any ambiguous part of speech.