How do you handle a surprise complication occurring mid-treatment like a root fracture?

Patient: 37 year-old male with preventricular contractions of the heart not requiring medication

Chief Complaint: Toothache with an upper right back tooth painful to touch

Dental History: The patient reported having had root canal treatment and a crown restoration on tooth on the maxillary right first molar (tooth #3) an unknown number of years previously. He had developed pain two weeks before the examination by the author. His dentist had attempted to adjust his night guard with failed to alleviate the pain which prompted the referral.