This will only happen if they are pretty much killing Smackdown! for good, with the move to Friday Nights, because I still believe Batista or HHH will go to SD! with the belt.
But if this were to happen, I could see Angle and HBK have a classic match at Vengeance, with HBK winning and offering a handshake to Angle after the match. Angle accepts, gets cheers, whatever. Later that night during the HHH/Batista match, Flair is helping out HHH, which draws out HBK to help (maybe a he confronted Flair before some match, or it really doesn't matter, they don't like each other anyway) out Batista. He beats on Flair, but HHH knocks down HBK. HHH gets the sledgehammer, and this draws out Angle. HHH sees Angle, and stops his movement. HBK gets up, and HHH just stares at them. Flair rolls back into the ring, to even up the odds, but all four men just smile as Batista gets up slowly inbetween them (I guess he got his ass kicked badly). HHH hits him with the sledge, then it's a beatdown, with HHH obviously winning the title.
That's how I'd book it.