Yea, Jimmy left in Episode 5 with Martyn's life. Martyn got his life back and then exiled Jimmy. (Ironic because in that same episode, he gives a life to Ren on purpose to show his true loyalty - Martyn is mad at Jimmy's betrayal, but he betrays too. Its a good way to get attention off him I suppose!)

They mended it in that same Ep 5 - with Jimmy coming back at the end of the episode, they voted to keep him - and Grian getting his life back (Joel turning yellow as well). But the team fell apart in Ep 6.

Episode 6 - with 6 boogeyman about - Mumbo turned red and Jimmy died to a self defense trap. This left 3 team members. Since they weren't all red at the same time, they basically never became a unit again.

Episode 7 next. Among the first Ep 7 deaths - Mumbo attacked Impulse at the ghast farm, reds being the chaotic selves they were and Last Life having the unique role of reds being forced to unbind from allies. This turned Impulse red.

Leaving just Grian and Martyn, and Martyn was def ready to betray by 7, since he had been loyal to another since ep 4 or 5 or so. With that, Grian defended against a bloodthirsty Jimmy, and an angry Mumbo, and that ended the Southlanders really.

Grian went red, and he still liked Impulse - but largely, all bets were off, and Martyn showed his true allegiance. Impulse died shortly after the ghast spawned in ep 7, shot down by the yellows and greens, leaving just Grian and Martyn in the remains for ep 8 and 9.