Sounds like Horde fanfiction. Horde occupying Stormwind?
That is not going to happen.
Blizzard should instead carve new territory for the Allied races and do small scale race wars instead of full blown faction wars.
Some of the devs don’t want to do another Battle for Azeroth style faction war.
Trolls have motivation to stop the Alliance from learning Zhul’s secrets that steals the power of the Loa. Without the Loa the Trolls can be depowered and made weaker.
Forsaken could try and take pre-emptive strikes. Seems that Gilneans would take Gilneas back but the Forsaken violated Kul Tiras as well, So some human kingdoms will want to make sure they won’t become Forsaken in death.
Maghar might cause the Alliance to return to Draenor. They were defeated by High Exarch Yrel. So if the Horde was to go back to Draenor on behalf of the Maghar then the Alliance can’t just leave High Exarch Yrel to take them on alone.
The Kul Tiran tidesages and shaman going to Pandaria to seek out Immerseus to try and restore territories plagued by the Forsaken.
Then the Night Elf people that have always been savages might want revenge once they get their new Tree back made from the souls of those the Horde burned with Teldrassil.
There would always be reasons for conflicts.
But lets be realistic. Horde are not strong enough to occupy Stormwind. Horde are worse off after the 4th war and are still recovering.