Imo Sasha didn't kill herself to ruin Negan's plan. Her negotiation with him about the number of deaths was the clue. She always intended for herself to be the one death because she made it clear she didn't want Negan to use her to get the upper hand. And in that she succeeded. Negan couldn't use her and the surprise of her being a zombie turned the tables at the perfect moment. So in a way she won and accomplished exactly what she set out to do. If course her killing Negan would have been the icing on the cake but if there is anything the walking dead is about it is serving cake with nothing but **** smeared on it with turd sprinkles.
Yeah, the show has really started going in circles. The only other option is for them to live in peace and harmony which isn't much of a show, so I think they're stuck.
Maybe next season Daryl will jump a pool of zombie sharks on his motorcycle?