He shouldn't be surprised, really. He knew when he'd stepped in to the room that it would either be him or Lucifer; his bet was on himself. He knew he wouldn't be able to come back. He knew that it would be the end of his previously immortal existence. He knew a lot of things. And here he was, half slumped on the floor, Lucifer pressing the knife in to his vessel, and in to his celestial self. It hurt, but it hurt worse because it was his own brother. Okay, sure, he had been aiming to kill Lucifer a few minutes ago, but it still hurt none the less. As his eyes found Lucifer's, a sudden, unfamiliar sense came over him. Was he scared? He'd never been scared before in his entire existence. Never. Not once. There'd maybe been once or twice when he'd gotten a little nervous, flustered even, but never scared.
Death was something he's never really come to terms with, because he'd assumed he'd never have needed to. And he especially never assumed that he would die at his brother's hands. When he'd told Lucifer that he loved him, he'd really meant it. He hadn't wanted to hurt Lucifer either, but he knew it was all for the greater good. Ha. The greater good. He'd seen many of his brothers and sisters die for the greater good; he'd seen Castiel flip off Heaven for the greater good – ostensibly, the Winchesters were the greater good. This was one of the reasons he'd left the family feud and become a Trickster in the first place: he hated the sibling rivalry, yeah, but he'd also hated the idea of having to sacrifice everything for a cause that his Father deemed good.
Like all other stabbed and dying angels, there is next to no blood from the knife. His brother's arm is around his waist supporting him for a few tormenting moments. Lucifer's other hand is still clasped tightly around the knife's grip, plunging it deeper inside of him. He is vaguely aware that Lucifer is speaking to him, but he can hardly hear a word. Maybe he's choosing not to listen. For a moment, he thinks about what must, or at the very least what should have been going through his brother's mind as he stood there, leaning over his sibling. He wants to believe that Lucifer deeply regretted this, regretted all of this, but he knows differently. He knows Lucifer all too well. In a desperate attempt at grasping consciousness, his mind pulls him back to Sam and Dean and the greater good. What an amazing choice for last thoughts.
Although he'd never admit it out loud, he envied what struggling, broken relationship Sam and Dean had: at least they'd managed not to kill each other. That was a definite step up from the current situation the archangel found himself in. He recalled a time, decades and centauries and millenniums ago, when he, Lucifer, Michael and Raphael had all lived in a perfect, organized, neat sort of peace. Back before Lucifer fell. Back before Heaven turned in to a battleground. He'd been happy then. He'd also been happy when he left all of that behind. But now he was here, dying for a cause he hadn't wanted to be a part of less than a day ago. He thinks for a minute that Lucifer will apologize, say one last comfort to his dying brother, but that's all too much of a fluffy dream. And he's one to know about the falsehood of dreams – a good portion of his life was spent dreaming that things would be better. They never did get better.
Being the always cheerful presence that he was, he forced himself to think on the bright side. At least he wouldn't have to deal with everything anymore. 'Everything' being Lucifer, Michael, and the Winchesters. Unfortunately, being dead meant no more Trickster-ing, and no more candy. And God knows Gabriel loved candy. And then he remembered – there was no God. Dear old Dad had gotten up and left, leaving his kids to tear each other to shreds and basically destroy what was left of the family. Sometimes he wondered if Dad resented the fact that he'd left Heaven, but now wasn't the time to start caring. God was gone, and he was dying, and his brother was killing him. But that raised an interesting question: he was dying – what should he be caring about? If not his life (that was long gone), not his family (that was even farther gone), and not the 'greater good', then what? It was in the middle of this particular thought that Lucifer chose to twist the knife.
Then he finally felt that searing, white hot pain of the knife truly piercing him.
And that was the last thing the archangel Gabriel ever felt.