A Yes Man/House victory would screw the NCR but good, but they would probably be better off in the long term assuming the electorate uses this opportunity to rid themselves of Kimball and his greedy and stupid friends. With New Vegas as a buffer state between them and the Legion they would have time to get thier house in order and expand North or South when they are able to support the effort properly. Or a Civil War could erupt over who got to chart the NCR's future course. Perhaps someone will help make a decision whether the NCR will return to it's roots and look out ofr everyone or become sham Republic ruled by a oligarchy devoted to military adventurism.....
If the Legion wins, the NCR would be well and truly screwed, as Caesar intended to prosecute the war with the NCR until it was destroyed....and it's last leaders paraded in Triumph down the Strip before being hauled off and crucified.....then he would build his new Empire on top of it's rubble. With the NCR's forces in the Mojave routed or annihilated, and Kimball and his friends totally discredited, the NCR might even fall into a Civil War over how to deal with the situation. A perfect situation for a anti-hero reluctantly serving a fascist Regime because the only alternative is even worse 40K/Halo/Gears of War style.