The issue is that the military knows it cannot be in charge, the days of coups being relatively accepted went with Cold war era politics. It's now a game of brinkmanship, Mugabe's hand is strengthened by the fact that Chiwenga cannot legitimately present himself as the defacto leader because SA can just push the region to isolate Zimbabwe. I am not sure they can force Mnangagwa back as VP because how will that relationship work, if the army fails how many of those guys will remain alive or even in the country. They had the head of the army and air force at their presser. They can try for limiting Mugabe's power but he will argue that he has the law on his side because he is empowered to take all the actions he took. The political side is all that is left, and if they continue to arrest Grace's allies like Jonathan Moyo and Kasukuwere who were the ring leaders they can live with a weakened Grace.