Locking the thread not be a good decision and just like you said if the thread becomes a spam ground and no update from the admin it will be better to get it locked. But if the admin will appoint a representative to answer people around here.
You are right that locking the thread won't be a wise decision and also if no representative appears on here still community will take part on the conversation which will keep active this thread. To avoid spam thread creator could do the same which can a user of the forum can do.