As I said, if they can't trade Sutter, I question whether they should sign Beagle at all. But let's leave that for later. Let's first consider what happens if they sign Roussel, and assume Pettersson makes the team out of camp. Virtanen is a lock and won't be traded.
Baertschi-Horvat-Boeser
xxxx-xxxx-Virtanen
Eriksson-Sutter-Pettersson
Rousel-Gagner-Granlund
yyyy
yyyy
That leaves 4 spots open: two in the line-up and the 13th and 14th forwards. These four spots will be fought over by Gaunce, Leipsic, Goldobin, Gaudette, and Dahlen. It is more likely than not that Dahlen will start in the AHL where he should be. So you have:
Baertschi-Horvat-Boeser
Goldobin/Leipsic-Gaudette-Virtanen
Eriksson-Sutter-Pettersson
Rousel-Gagner-Granlund
Gaunce
Leipsic/Goldobin
Under this scenario, injuries will occur and Dahlen will get plenty of opportunity at the NHL level, if he earns it.
I also hope that Gaunce can show he's an everyday player and displaces Gagner to the press box.
One of Goldobin or Leipsic needs to step up.
I don't particularly like the roster but it gets the kids plenty of opportunity to play while pushing Gaunce, Goldobin and Leipsic to be better than replacement players.
Now, if Sutter is traded (highly unlikely but worth the effort to ask the question) and Beagle is signed, nothing changes much. Except that Beagle + assets returned for Sutter is likely much better than keeping Sutter.
This all assumes that the contracts for Roussel and Beagle are two years or less, which probably means my entire post is irrelevant