Lit In what book did Obi-Wan's force ghost disappear?

Just want to know which book it was when he went away completely.

 

I believe it's Truce at Bukara.

 

Thank you

 

You're welcome.

 

It was actually Heir to the Empire, if I remember correctly.

 

You are correct:

"Luke?"
The voice came softly but insistently. Pausing amid the familiar landscape of Tatooine—familiar, yet oddly distorted—Luke Skywalker turned to look.
An equally familiar figure stood there watching him. "Hello, Ben," Luke said, his voice sounding sluggish in his ears. "Been a long time."
"It has indeed," Obi-Wan Kenobi said gravely. "And I'm afraid that it will be longer still until the next time. I've come to say good-bye, Luke."
The landscape seemed to tremble; and abruptly, a small part of Luke's mind remembered that he was asleep. Asleep in his suite in the Imperial Palace, and dreaming of Ben Kenobi.
"No, I'm not a dream," Ben assured him, answering Luke's unspoken thought. "But the distances separating us have become too great for me to appear to you in any other way. Now, even this last path is being closed to me."
"No," Luke heard himself say. "You can't leave us, Ben. We need you."
Ben's eyebrows lifted slightly, and a hint of his old smile touched his lips. "You don't need me, Luke. You are a Jedi, strong in the Force." The smile faded, and for a moment his eyes seemed to focus on something Luke couldn't see. "At any rate," he added quietly, "the decision is not mine to make. I have lingered too long already, and can no longer postpone my journey from this life to what lies beyond."
A memory stirred: Yoda on his deathbed, and Luke pleading with him not to die. Strong am I in the Force, the Jedi Master had told him softly. But not that strong.
"It is the pattern of all life to move on," Ben reminded him. "You, too, will face this same journey one day." Again, his attention drifted away, then returned. "You are strong in the Force, Luke, and with perseverance and discipline you will grow stronger still." His gaze hardened. "But you must never relax your guard. The Emperor is gone, but the dark side is still powerful. Never forget that."
"I won't," Luke promised.
Ben's face softened, and again he smiled. "You will yet face great dangers, Luke," he said. "But you will also find new allies, at times and places where you expect them least."
"New allies?" Luke echoed. "Who are they?"
The vision seemed to waver and become fainter. "And now, farewell," Ben said, as if he hadn't heard the question. "I loved you as a son, and as a student, and as a friend. Until we meet again, may the Force be with you."
"Ben—!"
But Ben turned, and the image faded... and in the dream, Luke knew he was gone. Then I am alone, he told himself. I am the last of the Jedi.
He seemed to hear Ben's voice, faint and indistinct, as if from a great distance. "Not the last of the old Jedi, Luke. The first of the new."

 

It is Heir to the Empire. Kenobi explains to Luke that he can no longer teach him.

 

Though he was in Edge of Victory 2 Rebirth and The Unifying Force from the NJO.

 

Obi-Wan? I can't recall those scenes - quotes?

 

According to Wookiepedia anyway

 

The Rebirth scene's a bit more ambiguous:

p272:

All futures exist in the Force, a familiar, impossible voice suddenly said. You do not choose the future so much as it chooses you. Do not look for answers there.
"Ben?" Luke croaked, stunned. It couldn't be Ben, of course. That time was long gone, and his old Master was truly one with the Force, unreachable, and yet ...
But it didn't matter whether it was Ben, the Force, or part of Luke himself that had just spoken. It only mattered that he had glimpsed what might be, and only the tiniest part of it, but it was only what might be.

The The Unifying Force reference was pretty clear that Luke thinks the familiar voice speaking to him at that moment, is Obi-Wan though.