Maybe this could happen, but for me i think if this cash will extinct, more bad elements will surely grab the chance to use fraud online payments during every transactions. It can be also a security from hold-ups, theft and robbery.
Exactly, being digital dont assure you maximum times whether you are doing right transactions or not. Like you all better know about the cyber robberies and thefts all around the world. So bitcoin must be impaired with cash else, if you are thinking about a society that dont use cash, that will not stabilize itself for a longer time. Cash is compulsory and you are right it cant be distinct.