It will take more than a year to make these coins disappear. Think about it, coins like Ripple are highly centralized, and you see no one using or talking about it besides pumpers and dumpers. Even so, it still has one of the highest market caps.
Not a year but more than a couple of year because a lot of altcoins that were created were from ICO that has more users supporting to it. Which means they have been holding those coins for a long time until they see the price to rise. Those at the top of the marketcap were from ICO's so basically it wasn't that easy to forget some of those coins, that were created by good developer and a hardworking manager.