Rabastan didn't even blink at the mood shift. Rodolphus was notorious for mercurial behavior, as his late wife was. "You want us to lead the charge? Where would we even begin? I've been gone too long; who's left?" He wasn't sure he was ready to jump into another all out war for Pure Blood supremacy, but, if Rodolphus wanted it, it would happen. Plus, this could maybe be a tribute to Bellatrix, for Rodolphus to move on.
"Excellent, and the laboratory? Have you been to see if it's in working order still?" He switched topics as seamlessly as his brother had.