Yes, there will always be a guy learning Latin or hand coding assably. That is not the same thing as a civilization retaining technical knowledge.
FOGBANK is the canonical counterexample: the US had made a nuclear weapons material before, still had the weapons, still had the labs, still had the budget, and still had to rediscover parts of the process because the tacit manufacturing knowledge had leaked away.
Yes, there will always be a guy learning Latin or hand coding assably. That is not the same thing as a civilization retaining technical knowledge.
FOGBANK is the canonical counterexample: the US had made a nuclear weapons material before, still had the weapons, still had the labs, still had the budget, and still had to rediscover parts of the process because the tacit manufacturing knowledge had leaked away.