I have firsthand experience with this.
In general, I believe recently I heard online sales are growing 3x faster than retail stores.
I personally am a merchant, so this topic is very important to me.
I was underselling the stores too much, so a company ( Skullcandy ) didn't want me to sell their products ( as I was hurting Best Buy, etc. ).
Stores are very upset, so they will try anything to stay in business. An online sales tax is coming.
It is quite funny when I see Best Buy / Walmart getting upset. They weren't complaining when they were putting small business stores out of business.
Where I live there used to be a street, probably over 100 years old, that used to be full of life. Then Walmart opened nearby. Now it is almost a ghost town.
I would say that people want things right away, so that will help. But with all these mobile devices, iPhone where you can order something so quick, I would say in 10-20 years, it will get worse, but not totally disappear.
Online will evolve, and consumers will trust online more, and want the best absolute deal. But there will always be a need for instant purchases, even if it declines.