You realise Westeros has... no real armies left. The armies have all been in war, most of the men are dead. THere wasn't an army left in the seven kingdoms who could actually stand up to them and the Dothraki, also the latter could have simply ridden out and gone raiding. No army would be mobile enough to run them down. The Lannisters were the rulers of the 7 kingdoms(or 6), yet there were basically every army so weakened that they had to hire the Golden company to even have any kind of chance and they were taken out as well.
Every major fleet was destroyed, the only ones left a few from Iron Islands and the unsullied still had a bunch of ships.
The unsullied/dothraki's were the major force left. The Lannister army (the biggest one) was literally destroyed, both at Kings Landing, at the castle where unsullied were somewhat ambushed but they still killed loads of Lannisters. The golden company is gone, the early war with Robb took out huge numbers from the north vs almost anyone supporting the Lannisters.
The Unsullied and Dothraki could have simply said we are the power, accept that, start rebuilding Kings Landing, bring provisions or we'll march on one of your kingdoms and take what we need.
The remaining military strength of Westeros is a complete unknown.
Cersei never ruled the Seven Kingdoms (or even six). She sat on the Iron Throne and ruled the Crownlands and The Rock. She gained some support from the Iron Islands through Euron Greyjoy, and some support from The Reach through Randall Tarly. But she never truly commanded either region.
At a minimum, Dorne's army is still in play, as are the armies of the remaining Reach Lords (e.g. Lord Hightower). House Manderly and some other Northern Lords still have some strength, as it's mentioned in (I think) S08E01 that they refused to send any more troops to Winterfell after the BOTB and the fall of The Wall. There's also a lot of Lords who are completely unaccounted for in the show, who may still be in play based on book trajectory (House Tarth, for example). Basically, a large chunk of Renly's army appears to have returned home and stayed there, following the death of their King. And many houses will have kept men back to defend their castles and cities. Episode 8 even introduces three significant Lords who we've never seen, suggesting that there are indeed some powerful players who remained on the sidelines.
On the other hand, the Dothraki are able to self-replicate, having been utterly destroyed in Episode 1 only for a few to reappear in Episode 5, and then hundreds in Episode 6. So I guess they would win. If there was an Episode 7, there would be thousands by then?
At the end of the day though, it doesn't really matter who would "win". Loads would die, on both sides. And for what? They were following Dany's dream. And that is dead now. They could kill loads of Westerosi. But they would never be able to rule there. The Unsullied have one huge disadvantage; they can't breed. Their numbers would fall every year, while the numbers of their enemies would grow.