1) 那您随便写!   discourse marker
2) 那我就给你做老婆。 discourse marker
3) 如果真的吓了你,那就对不起啦! This 那 refers to the preceding dependent clause.
4) 那可就完了!                                     This 那 has an antecedent.
5) 那好,这也算最理想的了。             This 那 has an antecedent.
6) 那就好!                                             This 那 has an antecedent.
7) 那要看是指什么。                             This 那 has an antecedent.
8) 那,那就先来五个吧!                     discourse marker
9) 那这次您就别打我了。                     discourse marker
My view is: 
The short form of 那么, ie. 那, has already been used discouse-marker-wise, or at least on the way of grammaticalizing to be a discourse marker. Other than discourse marker 那-prefacing, it can also be anaphoric.