Hello,Customer and thank your for asking your question on Just Answer.
An open bottle of soda pop does not spoil if not refrigerated, but it will lose its carbonation (fizz) much more quickly if not kept cold. In the refrigerator, with the bottle cap tightened well, the soda will stay pretty well carbonated for a day or two. Keeping the cap tight is very important.
Also, the less airspace between the top of the soda in the bottle and the top of the bottle, the longer the carbonation. This is because there isn't as much air for the carbon dioxide (carbonation) to escape into.
I hope this answers your question, but if you need further information, please let me know.
Thanks again for asking on Just Answer!