it is entirely possible that the bitcoin proprietors will change the protocol to no longer be deflationary; although that would cause some large-scale flight. I am not convinced of the keynsian model that inflation is exactly supply divided by velocity; nor of the 'crude austrian' model that inflation is function of supply only... If the demand goes to zero, so will the value.
While I think that bitcoin will recover, perpetual deflation is not guaranteed. Indeed, in general deflation of bitcoin depends on an increase in demand that outstrips the increase in supply.
I think the latter is naive. I think bitcoin is the first currency whose perpetual deflation is ensured by the contract that defines it.