Offensive production can (theoretically) be spread out. The Gophs may not have 1 receiver who did what Maxx did, but they can spread completions over several receivers - providing the young WR's and TE's are good enough to contribute. Same thing with the RB's - I don't expect any one RB to do what Cobb did, but if they can get production from 2 or 3 RB's, they should be able to collectively replace Cobb's yardage.
I think I also have to go with Wilson as the hardest to replace up front. A lot depends on Poock. if he's healthy, and is as good as they were talking about before the injury, the starting LB's should be OK. Depth may be an issue.
BUT - if the Gophs want to be the type of program that can be a consistent contender, then they need to develop the depth to a point where we're not wringing our hands every year, going "Oh, no - how will we ever replace the seniors?" Good programs have talent waiting in the wings to replace the seniors - or they bring in fresh talent from the HS and JUCO ranks.