I wouldn't count on having the return ticket reserved if you miss the outbound flight. I bought a round trip ticket last year DEN-HNL, planning to fly DEN-SFO-PEK-SFO-DEN then a day later do DEN-HNL. Well, due to a family emergency, I ended up flying straight to HNL from China, and so was only going to use the HNL-DEN return flight to get back to Colorado. I check My Itineraries multiple times, and my reservation was still there even though I had missed the outbound flight. I just happened to call UA the night before my flight back to Colorado, to check on something, and they told me my reservation had been canceled since I missed the outbound flight. I had to rebook, luckily there were still seats even though it was the night before.