He will be tough to replace, and he is better than the combo of Ogbole/Sommerville (even from those most optimistic about them), and he would have been a great compliment to this season's RU team.
But ...
Please, do NOT exaggerate his accomplishments: He did not average 12 ppg and 8 rpg for 3 years . He DID average that for 2 years - his Soph and Junior years ... and clearly regressed in every facet of his game last season as a Senior (except blocked shots - but was also not nearly as effective a defender - for whatever reason - every average or better center he faced last season out played him badly)
Freshman Year: 3.8 ppg, 4 rpg ... 63% FG, 42% FT
Sophomore Year: 11.9 ppg, 7.8 rpg ... 1.25 blocks/g ... 62% FG, 60% FT, 1-6 total from 3
Junior Year: 13.4 ppg, 9.8 rpg ... 2.1 blocks/g (though he was a far better defender this year than his Senior year) ... 51% FG, 60% FT, 4-22 total from 3
Senior Year: 10.4 ppg, 8.3 rpg ... 2.9 blocks/g ... 51% FG (really, should be better), 61% FT, 1-5 total from 3
Basically, Omoruyi made a big leap from his freshman to sophomore season, after Myles Johnson left, making Omoruyi the start - and visibly improved various skills, such as improved hands, better shot selection, better overall defense. He played at roughly the same level in his junior season, though with some improvements on the margin (32 assists vs 12 as a soph, more TO - 62 vs 41 as a soph but still a better A/TO ratio, 5% increase in minutes/game, significant rebounding improvement and a 1.5 ppg improvement).
But he really regressed last season, in hugely important ways: Fewer rebounds, much worse on-ball post defense, significant reduction in FG% (even though he still mostly took short hooks, short turnarounds and dunks). You can explain away all that (i.e. no great shooters around him - vs as a Junior he had Spencer and as a Soph he had Harper), but the bottom line is that RU NEEDED him to step up his game and carry the team, as they did last year, he was completely unable to do so. Period, end of discussion. He could NOT be a "lead" player for RU - he just did not have the skills. He is a terrific complimentary player, not a star. I think that was proven.
I would remind people (and please someone correct me if I am wrong - I did this a week ago or so, and I think I got it right - or close to right at least): . When Omoruyi recorded a double-double last season (10 points AND 10 rebounds) in a single game, RU won ... period. 9-0 in the 9 games he was able to do that. Therefore 6-17 in games where he could NOT record a double-double. In many ways, you could say he was like Andre Hyatt: Very inconsistent, very good about 1/3 of the time. And sure, you cannot put it all on Omoruyi ... after all, mostly no other RU player stepped it up to carry the team in games where Omoruyi could not (except J. Williams a bit when he became available). Still ... a star player ought to be able to be better than carrying the team only 1/3 of the time, no?