How does Krakauer feel after achieving something he has been dreaming about for months?

Krakauer dreamed of ascending Everest for a lot longer than a few months.  Climbing was a an early passion of Krakauer's, so his dream of ascending Everest had been around for years. 

I dreamed of ascending Everest myself one day; By the time I was in my early twenties, climbing had become the focus of my existence to the exclusion of almost everything else.

Krakauer tried to convince himself that ascending Everest was no longer a dream of his.  His reasoning was that climbing Everest had become too easy and too commercialized.  

But at some point in my mid-twenties I abandoned my boyhood fantasy of climbing Everest By then it had become fashionable . . . I began to look down my nose at the world's highest mountain. Such snobbery was rooted in the fact that by the early 1980s, Everest' easiest line-via South Col and the Southeast Ridgehad been climbed more than a hundred times. My cohorts and I referred to the Southeast Ridge as the "Yak Route."

Krakauer admits a few paragraphs later that he was trying to convince himself that he didn't want to climb Everest.  He admits it, because when Outside magazine offered to bankroll his summit attempt, Krakauer barely even hesitated to accept.  

In truth, the call from Outside had unexpectedly aroused a powerful, long-buried desire. . .  In late February 1996, Bryant called to say that there was a place waiting for me on Rob Hall's upcoming Everest expedition. When he asked if I was sure I wanted to go through with this, I said yes without even pausing to catch my breath.

Krakauer did indeed make the summit of Everest, but by his own admission, he wasn't filled with wild explosions of joy and elation.  He was too tired for that, and too aware of the dangerous descent that he still had to do.  

Reaching the top of Everest is supposed to trigger a surge of intense elation; against long odds, after all, I had just attained a goal I'd coveted since childhood. But the summit was really only the halfway point. Any impulse I might have felt toward self-congratulation was extinguished by overwhelming apprehension about the long, dangerous descent that lay ahead.

His feelings of reaching the summit are closer to relief than joy.  

Perhaps your question is asking about how Krakauer felt after he had gotten back home.  Again, there isn't much joy in Krakauer over his accomplishment.  Sure, he feels accomplished that he was able to make the summit, but all of those feelings are tainted by a form of survivor's guilt.  Krakauer is glad to be alive, but feels horrible that he couldn't help save his friends.  

The stain this has left on my psyche is not the sort of thing that washes off after a few months of grief and guilt-ridden self reproach.