Jack Crusher's death is vividly described in the Star Trek novel TNG: Reunion (not to be confused with the episode of the same name). In short, there's considerable tension between Picard and Beverley because Picard not only ordered Jack Crusher into danger but also because he rescued another crewmember when they both got into danger, leaving Jack to die.
You've heard the story about how Jack was killed, right? About the
problem with the nacelle, and how we had to go out there and sever it?
How the energy buildup overcame us, and Jack died in the explosion?"
Crusher nodded. "Of course."
"Well, it didn't exactly happen the way you heard."
The doctor felt the blood drain from her face.
"What do you mean?" Joseph thrust his chin out. "I mean, Jack didn't
have to die." He paused.
"It was because of me that he got killed. Because of me.
"He didn't. He stayed out there, cutting at the assembly--comtrying to
do it by himself. More than halfway to the hatch, I looked back and
saw him." Joseph's brows came together into a twisted knot. "I'll
never forget it. There he was, blasting away like he couldn't stop."
Pug's eyes went wide. "And the energy leak from the nacelle was
getting worse. It looked like something alive, some-thing fierce-like
the bloody Angel of Death or some-thing. But he'd done some damage. It
looked as if he was close to severing the nacelle entirely. Maybe with
a little help from me, he would have. "Suddenly, without warning, the
energy leak began accelerating-- growing like crazy. It was obvious
that something was going to blow. But Jack didn't budge.
He kept firing his rifle, even though you couldn't even see the phaser
beam anymore for all the radiation pounding at him. He must have known
how near he was to accomplishing his mission. And while he was trying
to blast away the last of the assembly, I started moving again toward the hatch-even more
out-of-my-head frantic than before. As fast as I was going, I should
have gotten tangled up in my grapples. Somehow, I didn't."
Joseph bent his head again, ran his fingers through his closely
cropped hair. "Then I saw the captain coming from the other direction,
and I realized what I'd done. And I knew what the others would say
about me-how I chickened out, how I lost my nerve. I couldn't stand
the thought of that, I couldn't.
So I just went limp, just pretended I was unconscious. It was all I
could think of.
"I didn't expect him to drag me back. I thought he'd go after Jack-
come after his friend. But I was closer, I was a sure thing. A part of me
wanted to tell him I didn't need his help, that he should have gone
after the other guy to talk some sense into him.
But then he would have known I was a coward, and he would have told
everyone else. So I stayed quiet.
"When the energy pocket exploded, we were sheltered from the impact.
All I saw of the blast was the radiation from it, and then the
nacelle, or what was left of it, spiralling off into space. And I knew Jack was gone. The Captain knew it, too