That’s a different game. Horde vs. Alliance was the whole point, and it can only end in Horde victory. This was always true, as the Alliance has never been as popular as the Horde, and at some point, everyone knew the Horde had to win. This was the most likely way for it to happen - attrition.
There will need to be some more plot written, but eventually, the Alliance needs to fall apart canonically, and the more-peaceful Horde can be there to support the remains of their old enemy, incorporating them into the fold and truly ending the divide. It’s the only way that makes sense.