A big part of WoM will (I hope) be insanely powerful heros who can zap a enemy unit with a single thunderbolt. So even if they tried to make battles like in Total War, it wouldn't play out that way.
I agree with what pigeon said about the emotional involvement we might feel in TW-like combat with any enemy dragon bearing down on us. But I really, really agree with what others said about TW battles taking too long and getting boring. And I agree with Demiansky that MOM battles are still fun after all these years.
Maybe if they make autoresolve NOT be "auto-lose", and made the AI less stupid, battles might be more fun and more possible to avoid, so they could do anything they want with the details of the battle system without ruining the game.
Meanwhile, the dev journal said back in July that battles would be "continuous turns", not RTW. I *guess* that would fit better into some sort of grid.