Not necessarily. If Prinz Poldi continues his amazing form shown in the last two forms, Reus won't be missed that much.
As to Marco, it is the story of his life. I remember he got injured right before the Euro 2012 too.
Poldi has been pretty good and looks like he really wants to get stuff done.
Still, him or Schürrle will be a huge downgrade from Reus.
Also, Reus never got injured before the european championships in 2012.
It was just Löw playing Podolski instead of him and especially that semifinal against an Italian side that had trouble at defending the wings showed how stupid that was.
Anyways, today loads of German news outlets are reporting about Reus and Barca having agreed on terms but that no one knows if the club will sell him.
They also state that Barca's offering 35 mil euros(the exact amount of money he can leave for next summer) and if that's true, then Dortmund won't sell him for that price.