The HFC was in one issue... They were these rich people that funded Xavier's school and were throwing in their chips for the Phoenix and Sebastian Shaw waited until Jean's powers to freak to capture them. He conjured the Phoenix and his death as well. Nothing really was done wit them after that.
That's good. That is, if he were to build them up and have them as formidable villains... If they were in one double-sized issue and they die, that's a waste. Millar did wrong with them AND the Phoenix.