I'm going to assume this offensive falls short for this season. What I worry about is can Russia then rebuild another defensive line that is as strong as the one they built last winter? They must've laid hundreds of thousands of mines, and used all kinds of materials and men to build trenches, dragons teeth, etc. Their supplies can't be unlimited. Now if they only have to build new lines around the "dents" in their original lines then it's far more feasible.