The o-line could potentially lose Schlueter, Olson, Dunlap, Faalele, Andries and Schmitz. Schlueter and Olson have already been here 5 years, are they going to come back for a 6th? They are both solid, but could test the NFL waters or move on. Faalele, Dunlap and Andries have now all been here 3-4 years. It's not inconceivable that two of them would test the NFL - I think Faalele and Dunlap would get drafted based on potential alone. And Schmitz is a junior and was name HM all B1G.
I doubt all 6 leave, but it won't be surprising if only 2-3 of them are back.