Can a party choose to do a mediation over the phone after it was scheduled to be done in person?

A mediation is scheduled for my husband and the mother of his son. Three days prior to this appointment, that was scheduled more than a month ago, she called and said she needs to reschedule because she will be out of town. My husband lives in MN, she in MO, and the mediation is in MO. My husband asked to have the date of the mediation be the same as his pick up date for summer visitation so it could all be done with one trip. She agreed to the date and now is claiming to be out of town on that date. She told my husband to pick up his son where she will be and that she will do the mediation over the phone. It was agreed upon to be done in person because the level of conflict they have is quite intense and more could be accomplished in person. Per the court order she is required to bring the son here if she isn't in her normal location on the date of pickup. The mediator will call tomorrow, hopefully to anwer his questions, but we are looking to see if anyone knows about this process now, as we have already booked and paid for hotels and train tickets to go to MO that can not be refunded.