The way I understand it, the Empire would have surely beaten back the Dominion, as a lone province (Hammerfell) was able to fight them to a stand-still. Seriously, the Empire is gone. It may exist in name and on paper, but it is truly gone.
Both the Empire and Dominion suffered heavy casualties in the Great War. With the Empire losing 3 legions and the remaining legions had lost over 50% of their legionnaires and the Dominion lost its main force at the Battle of Red Ring. I tend to think that both sides couldn't contiune the fight after that battle. Hammerfell was only able to fight back the Dominion due to two reasons, one being they facing an already weakened Dominion and the second being the legionnaires that were left behind to fight the Dominion which played an important rule of driving out the Dominion.
OT: I thought the Stormcloaks were traitors rather then freedom fighters, but you know the phase, "One man's terrorist is another man's freedom fighter."