Lofty and Tonker go off together and burn down the Girl's Working School.
Maladict also known as Maladicta is the only one of the regiment (besides Polly) to return to military life at the end of the novel, indicating that despite her cynical personality, she still wants to work for the ideals set out by Wazzer. Also, whether you see her and Polly's relationship as friendship or something else, it seems that reuniting with Pol was also part of Mal's motivation.
Word of God is that Mal did indeed return out of love for Polly.
Jackrum ran away to join the army in order to be with her sweetheart, and from the limited account we get, they seemed to make it work and be very happy together - right up until he got killed right next to her.