However, keep in mind that UA clears the upgrade list down to 2 seats in F at 24 hours out, and with other passengers moving around day of or booking last minute, it's pretty common for there to be no seats left in First the day of travel, especially on a major route like ORD-LAX. So while they could likely get rebooked same day if they miss their connection, it's far from certain they'd still be in First, if that's a major priority.