If I've been waitlisted, will I only get the offer if someone either rejects or reneges?

Hi. So I recently did a spd, and haven't heard back for almost a week. I am fairly certain that I am on the waitlist. I did pretty well imo, and was wondering if I am on the waitlist, will I only get the offer if someone either rejects or reneges? Will the firm extend offers if they find out they need more headcount? or will they circle back to the list and extend offers to candidates who should strong interest (and did well).