We have different definitions of "failure." Without the last 2000 years of philosophy, we wouldn't have formal logic, liberal democracy, the existential outlook, or any number of fundamental conceits that you and I use on a daily basis.
Whether or not any single fundamental question has been "solved" is irrelevant to progress in a field like philosophy.
To clarify, no the field is not based on social consensus but logic. How do we explain certain things? For example, Kant believed that logic as a field had been "solved" in the sense there needs no more progress in the field as the techniques developed were sufficient to solve logic problems. Until Godel came along and improved on logic in the 20th century. Solving in this sense is a technical definition not the social one.