You can record directly to a hard disk if you use a capture program that supports DVCPRO-HD streaming. FCP should be able to do it, for one example...
The HVX200's data rate is 100 megabits, which works out to about 1 gigabyte per minute, whether 1080 or 720.
If you shoot 720/24pN, it drops to 40 megabits per second, which works out to about 2.5 minutes per gigabyte. But you cannot stream that live to a hard disk, you'd have to capture that to P2 cards. One 64gb P2 card can hold 2.5 hours of 720pN footage. If you had two 64gb cards you should easily be able to capture the entire event, offloading one card while the other one continues to record.