Obviously rumors+allegations don't necessarily turn into verified violations, and even then, they don't necessarily turn into specific penalties, so Tressel may not be going anywhere after this year. But there is a chance he will, at least. If he does leave, who becomes their next coach? Some candidates:
1. Urban Meyer. Odds: 10-1
I think it's too early for Meyer to return to football, since he said he was going to spend time with his family. Plus he's not going to leave retirement for a program riddled with sanctions anyways. I just don't see this as likely, though the likelihood rises if Tressel sticks it out another year and/or OSU's penalties are light.
2. Luke Fickell. Odds 3-1.
If Tressel does get the boot this year, they'll likely pick a very solid, unspectacular, bean-counting, squeaky-clean true believer. Fickell is many of those things. If Fickell is not implicated in whatever causes Tressel to hypothetically leave, he's one of the prime candidates. If not, they'll have to look elsewhere.
3. Darrell Hazell. Odds 5-1.
Here's another possibility. Though he was on the program until recently, he will have been away for the Tatgate shenanigans fallout. Has most of the upside of Fickell too. Only problem is that he was literally just hired as Kent State's coach, and a one-and-done flight to OSU could create more attention than a hypothetically beleaguered OSU athletic department, conceivably seeking stability, wants.
4. Mark Dantonio. Odds 20-1.
I know some OSU bloggers are suggesting Dantonio, which would be funny in some ways, and not in others. He had no compunction leaving Cincinnati for MSU, so I doubt loyalty would be a factor. But I just don't see him leaving a stable MSU situation for an unstable OSU one (which is what it would be, in this hypothetical scenario).
5. Someone else. Odds 4-5.
As you can see, I think Fickell and Hazell are the most likely candidates, but both are almost certainly to be tarnished by whatever tarnishes might tarnish Tressel to the point where he goes. So I don't give them more that a 41.67% chance of becoming the next OSU coach...unless the violations end up not being as bad as the allegations and Tressel stays on. Then that likelihood increases.
But if, indeed, they are, then I think the chances of looking outside, perhaps for a former OSU assistant or another successful lower-division coach rises. Who are the likely candidates?