Gum swelling resolved on it's own - expensive treatment?

On Monday I went to an emergency dentist after experiencing painful swelling around an old crown for a few days. After scans the dentist identified no abcess but told me it was probably due to the crown being old and no longer adapted with too much space between the gum. He prescribed a mouthwash and endodontic treatment (take off crown, redo the root canal the' put a new crown). Last nigbt I awoke with a gross taste in my mouth and the pain has largely subsided as well as swelling, except at the very top of the gum near the cheek/ lip where it feels bruised.. If the pain / swelling has gone, does it make sense to do this very expensive endodontic treatment? Does the diagnosis sound correct to you or do you think the doctor is just trying to pocket a nice sum? This was not a dentist I know, but the only one available on Monday. Maybe I should cancel the surgery tomorrow and get a second opinion. Also, i'm slightly worried about not having taken any antibiotics for this. What's your advice for me? Thanks so much for your comments. I've had a lot of tooth problems for my age. I do my best to look after them. Surgery is expensive..