As COSPILOT notes, these are two separate tickets, so your AWARD flight - if you land after it departs at the "connecting" airport - would be characterized as a no show, likely resulting in the cancellation of your whole itinerary. It's not a TRIP IN VAIN, because the award ticket has nothing to do with the revenue ticket, and in this case, United's responsibility on the award flight starts at THAT AIRPORT with THAT AWARD TICKET. What you do prior is irrelevant to them.