If swelling goes down after root canal, is infection gone?

Possibly: During or after the root canal process, we often times looks for external signs that an infection is resolving. The lack of pain and swelling is a good sign. Unfortunately, antibiotics are also often given along with the treatment. Antibiotics can often mask the true success or failure of the root canal therapy. The best way to tell is to re-evaluate the root canal a year or so later.

Sign of healing: When swelling does down it means that the area is less inflamed which is a sign of healing. The infection may not be completely gone, but it is on its way out.

Can't answer: There is no answer for that question because swelling mostly goes down just taking antibiotics and the infection may still be active. Follow-up for at least a year and you will have the answer to your question.