Right now the Hossa-Heatley trade looks bad on the Sens part, but up until 2008, you could argue that the Senators won the trade.
The deal of Hossa and de Vries saved the Senators about $4 million when the cap was only at $39 million, and gave them a back to back 50 goal scorer in Heatley, who clearly had great chemistry with Spezza and Alfie, and gave the Sens much needed help on LW.
Ottawa needed cap relief, and while the way Muckler did it was wrong, if it wasn't Hossa traded, it most likely would've been Alfredsson out the door, and the return wouldn't have been a guy like Heatley, since at the time, it was thought that Alfie, who was 32-33 years old, would start to decline. I think Chara leaves regardless if Hossa remains in Ottawa or not, he wanted to be a captain, which Chiarelli knew and offered it to him in Boston when trying to get him to sign as a FA. Even if Alfie was dealt, a guy like Redden or Phillips would have been selected over Chara in 2005.
I'd say the trade started to look bad in 2008 or 2009, Heatley had his huge contract, and was beginning to decline rapidly, while Hossa put up a ton of points for the Penguins in the playoffs. Since going to Chicago, Hossa has remained a very solid 25 goal, 60 point player, winning three cups, while Heatley has bounced around between the Sharks, Wild, Ducks, and now AHL where he put up embarrassingly bad numbers between Norfolk and San Antonio (8 goals, 20 points in 43 games).