From my observations, advertising space is rarely a long-term commitment - especially for any one location.
Big business, small business, in fact ANY business will simply be looking for places to advertise that get the best return on investment ... and will be actively monitoring and seeking out ways to improve results.
Internet advertising is just another medium with a variety of opportunities that (I believe) are not too well understood - so there is a lot of exploration and experimentation ... with sufficient caution so as to not over-commit.
In a nutshell - if businesses use eBay and eBay does fall by the wayside, they will just find other avenues to continue.
But they will have taken note of how well certain things did or didn't work - and added those lessons to their portfolio of 'experience'.
(I have little doubt that there would be some businesses that would happily advertise on the side of a casket, knowing full well that it was a short-lived campaign and was destined to be buried.
Even 'dead men walking' could be lined up to wear Tshirts or carry sandwich boards.)
