Should one wait for his companion until the Dhuhr prayer is missed, or should he go pray?

One is not permitted to miss congregational prayers without a valid excuse. Therefore, if someone has an appointment, they must inform those present at the appointment location that they have gone to pray and that they (the others) should follow them or wait for them. If this is not possible, then attending the prayer takes precedence, because fulfilling a promise is considered mustahabb (recommended) by the majority of scholars. However, if going to the mosque would result in harm to one's person or property by leaving their companion waiting, then they are permitted to miss the prayer and wait for their colleague.