Lets just say that for some reason, the concept behind Twitter never gets off the ground. Yeah yeah, "and nothing of value was lost", but seriously, what would be the ramifications?
Do you mean the concept of twitter itself as a “microblogging” social media site or the concept of social media?
Because if it’s the concept of twitter itself as a site (140 characters, constant stream of posts, etc) then something else will fill the void. The genie is out of the bottle.