Never consider that Be'lal is alive. On the contrary, all say or imply that he is dead. This makes clear that Be'lal never showed up at any Forsaken meeting after his death. He also wasn't seen at all during the Cleansing. There is no reason to believe that Taim is Be'lal, because Taim's motives and knowledge would be even easier explained, if he was simply trained by a Forsaken (most likely by Ishy).