You did not have to spend the night at the airport. You could have paid out of pocket for a hotel, and then sought reimbursement from Southwest, or from your credit-card insurer if you charged the trip to a credit card which offers trip-delay insurance.

Can you explain what you mean when you said you had to buy two one-ways because your wife was not continuing on to SMF? Are you saying that if you used the companion pass for DAL-DEN-SMF, Southwest would not have let you board the DEN-SMF unless your wife boarded with you? Or did you have to buy separate tickets because your wife was checking baggage only as far as DEN?