I think one of the simplest reasons why Sales are not picking up is because consumers face a simple decision making process...what is termed as Routinsed Purchasing Behaviour....there is not too much thought which goes into it..this is mostly based on Money.....and since it is routinised it can result in brand switching for no real reason...hence thats why sales are not picking up.
If Pepsi was to suddenly move out of the market then yes definitely.
An increased demand for Pepsi will if you apply market logic result in a lower demand for coke and vise versa.
Its not really that the product is bad, ofcourse recent corporate messes have cropped up but there is nothing really different about this product., ....and unless it has a USP how will it stand out...... awareness through massive campaigns will not necessarily result in demand..
I personally prefer Pepsi...I have a reaction to coke..stomach pains!!
TC