I don't see Hart returning enough to make a trade worthwhile because goaltenders continue to be undervalued with the whole "goalies are voodoo" mindset. Plus, until the specific players under the Team Canada investigation are named, I expect that those who have not been emphatic and specific in their denials will have an asterisk on many GMs' trade target lists.
Honestly Hart is the only player I wouldn't trade, unless of course you get blown away by an offer.
The Flyers have waited a long time for stability in net, and it seems like things might finally be trending in that direction with Hart, Ersson, and possibly Fedotov or Kolosov. Hart is the only NHL-proven commodity and he's only 24. I hang on to him.
For TK, I wonder what kind of package he could return. Unless it's a top 10 (or even top 5) draft pick, the odds are that TK is a better player than the mid to late 1st rounder will ever be. On the other hand, TK is probably having a career year, and the Flyers will end up paying for past performance, so he is the epitome of selling high.
TDA is one I would absolutely try and move at the deadline. Obviously JVR and the other castaways too - Braun, Brown (all we need is a LeBrun to have "brown" in three languages).
Unfortunately, Fletcher is the one making the moves, and I don't think he's capable of getting maximum value.