This is only an educated guess and when the Cub Reporter/AZ Phil updates their 40 man we'll know for sure, but I believe Warren is in the same boat as Grimm and Brothers. They have options, but they have to pass through Optional Assignment Waivers (which are revocable) in order to be sent down. In the case of Brothers that's probably not a huge barrier, but it seems likely that someone would try to claim Grimm or Warren so it's probably best to assume they can't be sent to Iowa. For the sake of completeness, but at the risk of a rebuke from sneaky, Hendricks could still be sent down. he could, but i'll happily bet you this year's RK MLB 1st he won't be