Chris McCandless never had intentions of "never coming back". Look closely through the book and a bit in the movie and you are sure to find the proof. Chris had a gun on him and plenty of bullets left when he died. The fact that he suffered through the pain that dying the way he did brings, shows tremendous strength in character. He held on for as long as he could with hopes of being rescued.
Chris wrote Wayne that postcard to share his gratitude of all that Wayne had done for him. There was space to write it and Chris felt it needed to be written. He was building up the anticipation and drama of what really was a likely scenario which was that he could in fact die while on his journey. So the possibility was there but, the intention was not. Never was. This was nothing new, as Chris called a cave by the ocean in California his home for months before he ever stepped foot into Alaska. You may also recall Chris wrote several thank you good bye post cards to Jan as well.
Chris went to Alaska to sort through his own demons and most importantly for closure. The trip was to be nothing more than a one hundred day journey. This final trip to Alaska was not his first, but, was instead a repeated trip up there. He knew what he was getting into. He had a map. He had emergency cash and ID in a wallet hidden in his pack. Chris died of unfortunate incidents. NOT of poisoning, but, because he "held his breath too long". He could see in the reflections of the bus windows that he was quite gaunt and physically different in appearance than he was when he first arrived.
This added a dramatic flare to his story. Not only could he tell of the changes that had happened during his Great Alaskan Adventure but, he could easily show evidence of it's sacrifices through his physical appearance. He shaved on what he thought would be his last day. There's a message there. A message that clearly states Im going home now. Unfortunately what Chris didn't realize was that this change also brought with it significant weakness. A lack of strength mandatory to cross a river that was a mere stream when he first arrived.
There is no better option between that bus and the Tek. He returned to the bus not to give up but, because it was the next best option since crossing the river to get out wasn't an option at that time.
This is where the tragedy really began. It's called Rabbit Starvation. That along with lack of necessary daily caloric intake was his downfall. Rabbit Starvation if you haven't Googled it yet, is where your body simply starts to metabolize itself because you are eating lean meat with an absence of fat. Fat is needed to survive. Chris wasn't able to include it in his diet enough. To put it even more simply, Chris died because his body burned more calories than it consumed. It caught up to him. There were no poisonous seeds. There were no suicidal intentions.
He did die happy and it didn't regret being alone. That famous quote of "Happiness only real when shared" is a mere piece of a bigger statement. There IS evidence to prove my claim but, it's not my place to elaborate.
So friends, Chris McCandless didn't die unhappy. He died disappointedly aware of the fact that he would never be able to share his story as he had planned to. It was a surrender to God in the hopes that he would be forgiven and most importantly, understood.
The "Iris Fucyu" reference is found in the book and Wayne explained the reason. Chris wanted no part of IRS and the rules and bullshit that came with it. He worked at a casino in Vegas and used his real name on other forms as well.