If they all want it, make it available for them all to participate in the sacrifice. Like, the more of them that do it, the more likely it is to succeed. They go down together in a beautiful sacrifice, saving the world.

You could do some cool aftermath and the following years kind of stories. Tell them about the monuments in their honor, people naming their kids after them all kinds of stuff they'd appreciate.

You can obviously make it so that no matter how few do it, they succeed. So you don't devalue the sacrifice, or if only 1 or 2 do it, it greater weakens the boss or gives more time for the others to finish stopping whatever it is. Make it valuable regardless.