Their is a possibility for a major continuity problem to arise. From what I can tell, this series takes place immediately after The Lawless, and Talzin appears a whole bunch of episodes later in the Disappeared. If Talzin dies, they might have to change the chronology by pushing the Disappeared arc up a lot further.
Well Grievous doesn't get instantly owned by Maul, he actually doesn't get owned at all. Granted they only clash for like a panel (but it'd likely be longer if it were animated). Maul actually has to retreat since his army gets murked.
Also Dooku and Grievous are destroying Maul's powerbase so that he retreats to Talzin and then they can kill Talzin. Apparently Sidious and her have a history/ rivalry.