Does an RL agent need to experience a complete episode in order to learn?
If the agent gets no feedback whatsoever and has no information about the structure of the search space (just blind search, hoping to get lucky), then no, it can't learn.  It has nothing to learn from.  In your scenario, it has no information to enable it to improve: the feedback is always the same -- always an unending stream of -1,-1,-1,-1,-1,... unless it happens to get lucky.  Without feedback, there's no basis for learning.