I agree, ISU will be an early favorite to contend for a Big 12 title. They don't lose anyone from this year's team they can't easily replace. If Buddy returns, I think it will be one heck of a battle between KU, ISU and OU for the top spot.
KU loses Oubre, and likely Alexander, but Self will do his usual reload act in recruiting and the Jayhawks will be tough again. If Buddy comes back, I think the Sooners will be ranked no worse than the top three in the pre-season.