Dany built up the army and lost them (and her dragon) to the dead. She put on hold her claim for the throne which is what she wanted from the beginning.
None of them had a chance without her. Jon helped put all this together, but given the story we had. without Dany its absolute annihilation.
Debatable.
Lets say Daenerys doesnt exist. No Dragons, no Unsullied, no Dothraki. But... in the same token, the Night King wouldn't have got an undead Dragon to burn down the wall. Thus the first genuine battle would have been at the wall itself. The North would have been far more prepared to deal with that threat. Whether they'd have had enough troops to deal with that initial army is debatable though. I guess they would have had to smash their way through one of the wall entry points with a few of those undead giants. The battle itself would therefore have been pretty similar to the Wildling attack.
The size of the White Walker army would have been a bit smaller too given that they killed and resurrected a sizable number of people between the wall and Winterfell.