Hello Manata, first of all, I would like to thank you immensely for this guide, seeing as I am playing a Warsong Orc myself, so your work is really helpful to me to clear up things I did not yet know or had forgotten. Thank you!
Now, as to what happened to Ashenvale after Garrosh Hellscream was defeated, in A Good War it’s described that the Horde had pulled out of Mor’shan Ramparts atleast when Mop was over.
Within an hour, the convoy came within sight of the old Horde fortifications at the edge of the territory. A few years ago, Mor’shan Rampart had been the bulwark against the night elves pushing into the Barrens, but it had been abandoned when Garrosh Hellscream had been deposed.
There should have been night elves on those fortifications. There weren’t. Instead, there were two Horde rogues—an orc and a goblin—sitting comfortably on the structure, legs dangling in the air. They waved at the convoy as it approached, prompting another flurry of chatter among the army.
https://worldofwarcraft.com/en-us/story/short-story/a-good-war#tab=2
And Zoram’gar is apparently also a ruin when the Horde arrives there.
Saurfang ordered the army to set up a brief staging ground on the open shores near the ruins of Zoram’gar Outpost. The night elves would never leave the safety of the trees to attack an exposed space, so the Horde could repair their equipment, eat, drink, rest, and tend to their aches and pains without fear of reprisal.
https://worldofwarcraft.com/en-us/story/short-story/a-good-war#tab=4
So I think we can pretty safely assume here that the Horde in fact -did- abandon Ashenvale after Garrosh was dethroned. Hope this clears that up!