They have already started to drill a relief well, so it will stop at some point... and this has happened before and the Oceans aren't covered in oil.
http://www.nytimes.com/2010/05/03/us/03montara.html
"The Australian accident, known as the Montara spill, began Aug. 21 with a blowout of high-pressure oil similar to the one in the gulf. With the well spewing 17,000 to 85,000 gallons per day, precious weeks passed before the relief wells were started. When efforts got under way, the first four attempts — drilled on Oct. 6, 13, 17 and 24 — missed the original well.
A fifth attempt finally intersected the original on Nov. 1, and about 3,400 barrels of heavy mud were pumped through the relief well into the base of the original well. The spewing oil finally stopped Nov. 3 — more than 10 weeks after the original explosion."