I also think bitcoin will be replaced by something else in the future, but this does not have to be the near future.
Facebook is also still around, despite being "old" now. The key thing I guess is evolution of the technology, something that the replaces tech companies were ignorant off.
Well facebook taked down all the others social medias in a short time,offering all services and a full pack of games ,that made the most people use it,and keeps bringing new games and changing something,i believe they sucess keeps being huge the same way as whatsapp just killed the previous sms fee service,now you can talk unlimited to anyone without have to pay a fee evertyme you reply .With bitcoin i believe its very hard to replace or to reach bitcoin status that is very high and witha huge support at it.