No it's the other way around. The Dwarves can and have done fine on their own, it's only a few surfer trader houses that benefit from the surface trade, a fact that is brought up in the assembly, "without the surface trade half our houses would go broke."
World of Thedas page 35:
"Orzammar relies upon the surface not just for its prosperity, but for its survival. Ages of Bligths have taken thousands of thaigs away from the dwarves. These were the places where most of the food was raised. The dwarven kingdom that endured alone, independent beneath the Stone from time immemorial, perished in the First Blight, faded into myth. Now, the remaining dwarves in Orzammar cling to existence through a lifeline to the surface."
Orzammar would literally starve to death if human stopped selling food to them. And you think they're going to participate in the destruction of an kingdoms just because the Wardens asks?
The City elves are a strength, it is only human oppression that keeps them weak, but had they something to fight for they'd show it, and even without weapons we've seen them still rise up when they got fed up with the injustices. So don't put them down, when they are being offered a chance away from human oppression, and a chance at real self governing.
They were fighting silverite clad chevaliers with knives tied to sticks serving as spears and tables serving as shields. And zero training.
They may serve as arrow fodder and poorly at that, but that's it.
The Dalish have never turned away those who wish to return to the people.
First, you'd have to convince the Dalish attacking a human nation neighboring the most powerful empire on Thedas is a good idea.
Second, you'd have to be able to amass an army of Dalish from all over Thedas without raising suspicions and having the Chantry or the nations they'd have to pass to interfere.
Besides, the Dalish have already said they can't field armies. They can lead guerrila strikes but that will, hardly, lead to conquering cities with tall walls. They don't even have siege weapons.
Elves work closely to nobility, Anora herself keeps a handmaiden that is an Elf, as do many noblewomen, direct access to a potential ruler like Anora and Ferelden could again see yet another travesty befall it. City Elves would be the absolute first strike against the remaining human nobility, and after that total chaos.
Many? We've seen a grand total of two.
Are you really suggesting city elves could just assassinate entire noble families? Because that's silly.
Howe couldn't do it with an army.