Salam all. May Allah have mercy on us because we dont exact know what really did happen to the minds and intentions of some ashab of Mukhtar (r.a). I dont know how true it is but from one source i read that ibrahim al ashtar (May Allah forgive him) stayed in Mosul after hearing the martyrdom of Mukhtar (r.a). Aparently i also heard that when Mosab ibn zubair was againts abdulmalek ibn marwan, ibrahim al ashtar chose to be in Mosabs side againts abdulmalek. Therefore aparently i dont know nor neither can judge his intentions (only Allah swt knows) but its a sad truth that he has sided up with mosab in order to fight againts abdulmalek ibn marwan and he died in that war. I guess mosab gave him the guarantee of being the governor of Mosul. And only Allah knows.