Yeh it might be a possible caus if bitcome gain more popularity than liquid cash or any other kind of e-cash transfer..but this will not happen in near future..it may take long time for bitcom to gain popularity..
Its hard to believe that banks will completely disappear in future as banks are the most strongest financial institution that we have and comparatively bitcoin is very young and small and even if it becomes more popular in future there will be many people and businesses that will be dependent on banks for their transactions.
Banks are not very sound at the moment, many banks disappeared or were nationalized, a nice word to say the government rescue them with public funds, so if crisis was to strike again, something very likely, then many banks will disappear, not all of them but enough so people begin to wonder about the robustness of the world economy.