It depends. Among other things it depends on what data is going to be missing.

Thinking back to the bank there were some tables that we could do without during business hours but were critical for the overnight processes. There were other tables that we could do without for 3 weeks, but they had to be there (and complete) during the last week of the month. There were other tables where if the information in there was incomplete it was worse than if the system was completely offline.