While it is generally safe to keep a standing rib roast in the refrigerator for a few days, storing it for 6 days might not be ideal. The recommended storage time for raw beef, including rib roast, in the refrigerator is typically 3 to 5 days. After this period, the meat can start to lose its quality and safety.
If you need to store the rib roast for longer than 5 days, it's better to freeze it. When properly stored in the freezer, a rib roast can last for several months without a significant loss in quality. Make sure to wrap it tightly in freezer-safe packaging to prevent freezer burn.
Always follow safe food handling guidelines to ensure the meat stays fresh and safe to consume. If you have any doubts about the freshness or safety of the meat after storage, it's best to err on the side of caution and discard it.