I was under the distinct impression that this was only a test to gather data, and even if things go well, the cap is coming back off in 48 hours or less.
Edit: I can't remember the source for this; I believe I heard it on the Diane Rehm show yesterday. If I can find the source I'll update.
"BP cautioned that the oil cutoff, while welcomed, won't go beyond the 48 hours."
Yeah, you're right... it did go on to say that 'valves' will be opened and oil would be siphoned off. I didn't realize there were going to be pipes either. :)