I'm super high on him, but not so high that I think we should let Tiago walk.
Sacto demonstrated that he can't just walk out onto an NBA court and be effective -- he needs coaching. He should come in here as the 4th or 5th big initially, and have to earn PT as he acclimates. If he comes along really well, I could easily see him taking Boris's spot as the third big man at some point. If he comes along Kawhi Leonard style, I could see him getting starts ahead of Tiago by the end, but we still need a good big man who can bang with most centers and spell Tim, so dumping Tiago would be a big mistake. And, of course, if Robinson spends the year in Pop's doghouse, we still have our 3 best guys from last year.
If, by the end of the 2013-14, Robinson has somehow completely supplanted Tiago, it might make sense to put Tiago on the trade block next summer, but typically the market for centers who can do more than fog up a mirror is fairly robust.