Regulus felt as if he had been plunged into his worst nightmare, but there was no chance of waking up from this. He could run, of course; no one expected him to transform suddenly into a valiant warrior, willing to sacrifice his life for the greater good. Nor was he idealistic enough to think of this as an opportunity to atone for his past mistakes, closing some sort of cosmic circle.
But he knew he wouldn't run because he needed to do this - to face these fears - for himself. If he ran now, it wouldn't matter if Bellatrix and the Dark Lord were both destroyed today; they would still haunt him. If he stayed and did his best, then at least he could bury them in his own mind, no matter what the outcome.
He glanced around the room, sickened anew to discover Bellatrix was no longer alone; she had allies on the way.
"Rock would do little good against ghosts, I should think," he said. "A containment field would do much better, but we have a problem we must deal with first." He gestured to the other Death Eaters - Crouch and Goyle, among others - entering the room. "Bellatrix is no longer alone."