The plateau exists only if further investement is done and if new oil is found. If those two conditions are not met, the cliff will be much higher.

There is a very good editorial by Hugh Ebbutt a consultant in the UK that discusses what happens if your annalysis is correct.

"Those companies and people who eventually pull through this severe economic recession, after two or three years as the stronger parts of the world start growing again, may find themselves running straight into energy shortages that will have been made much worse by lower and slower investment now."

http://www.worldenergysource.com/wes/stores/1/Defining-Times-A-Chance-to...

Assuming those investments are not made, recovering from the decline rates may be impossible.