When he was defeated at Dyracchium and was forced to retreat, Caesar was about to be killed by one of his soldiers whom he was trying to lead back to fighting in order. His live was saved by a bodyguard who chopped the mutineer's arms off.
So I have no doubt that Marius or anybody else could have been murdered by one of his soldiers.
Many roman citizen soldiers, including loyal supporters, were fed-up fighting on and on and on again and had the feeling of being "cannon fodder" wasted for the sake of nobles' rivalries.
This is why they suite often mutinied, or killed their general or deserted to the winning side or, when the y were on the winning side, slaughtered many of their enemies in order to hasten the end of the civil war. The men wanted to save their lives and the best way to save their lives was ending the civil war quickly.