I think it depends on your definition of fail.
Will it become a viable currency. Yes I think so.
Will it become centralized, and controlled by a handful of powerful (and wealthy) people. Yes I think so.
Bitcoin will be a successful currency, but we will simply swap one unaccountable entity (central banks), for another.
Try not to use common sense here. It just pisses everyone off.
Bitcoin doesn't have to be used by everyone in the world or replace all government currencies to be a success. Even if it just captures a share of the money transfer business away from Western Union it's successful. Businesses and criminals alike have already made millions of dollars with Bitcoin so it's already a success for them.