The Phillies would want to substitute either Drabek or Happ with another pitcher, Carlos Carrasco. According to Andy Martino, a Blue Jays assistant was on hand to watch Carrasco pitch 6 innings and give up 6 runs... Not a good impression Mr. Carrasco.
The Phillies will have to include 4 or 5 players in a deal for Halladay if they do not put both Happ and Drabek in the deal. Those players could include Carlos Carrasco, Lou Marson, and/or Jason Donald. We're just going to have to wait and see.
This deal better get done. The Phillies are in a perfect situation to aquire Roy Halladay. They have good enough prospects to get him, and they have enough prospects that, if they get him, their farm system is still not depleted. If the Phillies can't make this deal, they can't make a deal with anybody!