I liked Schiano, and I feel he did a great job here bringing us from the depths to respectability. There are some concerns, though, about bringing him back.
1. People talk about his recruiting being great, but I don't remember that - maybe it was just "great" in comparison to what we'd seen prior with Shea and the early Schiano years. From 2006-2010 (beginning when the team started to have some success in 2005, but ending before Hafley showed up), he had 13 4* guys and no 5* guys... about 2.5 per year. Half did well: Britt, Abreu, Davis, Vallone, Holmes, Ryan, Coleman (4 of 7 were defensive guys). Half didn't do so well: Robinson, Young, Forst, Stroud, Savage, Williams (all offensive guys). Our recruiting rankings over those five years were: 42, 37, 46, 38, 64.
Once Hafley showed up, the fortunes changed a bit. In 2011-12 we had 8 4* and 1 5* guy, or about 4.5/year (almost double the top prospects that Schiano had been bringing in). Our rankings in those two years were 32 and 24.
If we bring Schiano back, I really hope we're able to get Hafley back on staff, too.
2. Schiano struggled with developing quarterbacks. Teel took over in 2006, and we had effectively no backup until he graduated (the Jabu package isn't really a backup QB). After that, it was musical QBs... Natale, Savage, Dodd, Nova. Flood really wasn't any better in this arena... though Friedgen helped Nova a lot in his senior year, I think.
If we bring Schiano back, I really hope we're able to get a QB coach or OC who is able to develop QB talent.
3. The offense was usually just an extension of the defense. Schiano plays ball control offense, killing as much clock as possible and rarely airing the ball out. He kept his defense off the field as long as possible to keep them rested, but that usually meant we weren't scoring a ton of points. Without a star RB like Rice who could consistently move the chains on the ground, that type of offense doesn't always work out so well. We'd need a strong OC to pair with Schiano, who wouldn't be afraid to challenge him.... though Schiano tended to churn through OCs, so that might be hard.
4. The defense was undersized. While this worked in the Big East, the Big Ten is filled with a lot more bruisers on offense - especially in the trenches. We'd need to pivot to bigger DLinemen at the very least, but also likely bigger LBs.