The land and oceans "switching places" would mean the end of life, as we know it. However, this is quite unlikely. A more realistic scenario is the rising of the oceans, due to the planet warming, and the impact that will have in the future. Most climate scientists agree that at some point in the future, the U.S. will lose about 17% of its present land mass...and low lying coastal cities along the Gulf coast, and Eastern seaboard, and all of Florida, will be under water.
This will result in the loss of trillions of dollars of real estate, and infrastructure, and 10's of millions of coastal residents will be forced to migrate further inland. That will create chaos like we've never seen before.