Turner Ward
This is cheating a bit, but how could we not throw Tuner Ward into the mix as someone who should be coaching his last series with the Cardinals this weekend?
If you want to throw Oli Marmol, John Mozeliak, Dusty Blake, or whoever else into this mix as well, go for it. But the only one that I have to say without a shadow of a doubt must be let go is Ward at this point.
Mozeliak, even if he steps aside next week and lets Chaim Bloom take control, will still be under contract and around in some capacity, so I don't think it makes sense to say he should be on this list. Marmol, I would argue, has done well this year, and while I wouldn't be opposed to firing him, I don't find it to be necessary. While the Major League pitching has not been amazing (at least in the rotation), Blake has been credited with helping transform how their minor league pitchers are developing.
Ward, on the other hand, has seen a talented group of bats underperform under his leadership for two straight seasons. Both veterans and young guys are seemingly regressing at the plate year to year, and their historically bad numbers with runners in scoring position is inexcusable.
This group of position players should not have been a bottom 10 unit in baseball this year. There is no way the front office can bring back their current group of hitting instructors, at least at the Major League level, and convince fans they want to turn things around.