Boyd is good, but I have no doubt that by next year Quay Evans will be better. And if Nick James buys in, we'll be golden. Lawrence is good, but there are a lot of guys we can slide in there from a talent standpoint and be just fine (Wells, Bohanna, Hughes, Brown(s)). Leadership wise, maybe that's an issue. In the secondary, we don't play a lot of man anyway and so while we won't be as good in the back end, I am perfectly confident that Calhoun, Love, Giles can fill in well in the zone schemes.
On offense, we lose Green, Bumphis, Smith, Clark, Heavens. We will return EVERYONE on the OL. We will return a 5th year senior quarterback, and we will have several receivers who have played a lot in college ready to step in (Lewis, R. Johnson, hopefully Morrow matures). All our RBs will be back (unless there's depth-chart related attrition). At TE, we'll be more than OK. Malcolm Johnson and Brandon Hill will be very nice weapons.
While I wouldn't say we'll definitely be better, I think maintaining our current level is a very reasonable expectation. Every year everyone has to replace players; that can't be an excuse, because anyone could say that every year.