Axford had an OK season in 2015, but the walks continued to be a problem for him. He's probably iffy as a closing option at this point, but there are major league bullpens that will be happy to have his arm for the late innings. Rex Brothers is another interesting case. The lefty has always had trouble with walks. He imploded to the point that he ended up spending most of 2015 in the minor leagues. He came back and posted good results, but had 8 walks to only 5 strikeouts in about 11 innings. Both will get a guaranteed Major League deal most likely.
Kahnle has pretty much been just a replacement level middle reliever and will probably latch on with another major league organization on a minor league deal. Rosario has put up some significant power numbers in the past, but he's a negative defensively. Some organization may look to see if he can rebound offensively.
The moves are expected to save the Rockies roughly $11 million, per MLB Trade Rumors’s arbitration projections. With the Rockies needing to upgrade in a number of positions, relief pitching understandably isn't a priority at the moment, especially all guys with minimal upside.