The 04-05 Senators would have had Redden, Chara, Phillips, Pothier, Volchenkov, de Vries as the top six, possibly Schubert as the seventh, with a guy like Todd Simpson brought back (think he was a FA after 2004 though) for depth. Meszaros likely stays with his WHL team as a 19 year old.
Offensively, the Sens had Hossa, Alfredsson, Havlat, Schaefer, Varada, Vermette, Kelly, Smolinski, Spezza, Langfeld, Neil returning from the 03-04 team. Bonk was traded to LA (then to MTL) at the draft, as Spezza would be ready to take his spot on the team. White was gone too. Not sure if the Sens would have tried to bring back Bondra, as I think he was a FA after the 03-04 season. Bochneski would have tried to crack the 04-05 lineup, as well as Patrick Eaves.
Goaltending was Hasek, as Lalime was traded to the Blues, and perhaps Prusek is brought back as a backup, as I think he was a FA after 03-04. I think the Sens keep Emery in Binghamton and if Prusek isn't brought back, they sign a veteran back-up goaltender just in case.
Coaching would have been Bryan Murray, as Martin was fired after losing to Toronto again.
Obviously if there was a season, other changes would have been made, but I think Eugene would have opened up his bank account for the Sens to sign pretty much whoever they needed, as this team was a legitimate Cup contender.