In no particular order ... LJH, Omenihu, Anderson.
Been said already upthread that the really cool thing right now is that we have backups to actually fill some of these spots, unlike the last goddamn decade. Coburn fills in neatly for Nelson. There will be a dropoff, but it's not a guy playing out of position. The LB and CB positions are similar. There will be a dropoff, but there are highly-rated guys ready to stand in. LJH and Omenihu are difference-makers, and there's just no way around the fact that when NFL talent leaves, you feel it. So that's my answer.
Agree with Beck and Watson as well. Those two guys are cogs in this wheel - Beck made so much of the offense go beyond just his offensive output. He stabilized a position that was a literal black hole for years. Watson didn't fumble. Period, end of story. Kirk Johnson, to the bat phone - this is how you get on the field next year.