I'm gonna be honest. The NCR is my favorite faction in Fallout. I will give an honest thought to what I think and not because they're the best. The NCR suffer from political corruption,traitorism and much more. But they are probably the best thing that could happen to the Wasteland. They are actively trying to restore the United States to its before war glory. The Brotherhood hasn't done much to the wasteland and just because a splinter faction breaks off and starts helping doesn't mean they are now better. I don't think the NCR will be able to reclaim all of the United States. But I think they can conquer the Entire West Coast and Form a nation there and try to expand further east when they know they can. As for after what happened in NV, I say the NCR wins but does not control New Vegas. The NCR probably stops trying to expand so they can focus developing mostly because of the heavy loses fighting Caesars legion and raiders. They may try to befriend the Mojave Chapter of the Brotherhood and a possible Alliance between the two. The NCR continues building its Military and Develops the Mojave(And whatever territories that aren't) and finish cleaning up any remnants or false groups of Caesar's legion. After that they just need to keep the Raider Population to a minimum and keep fighting the Corruption. So do I think the NCR will be the Dominant Power? No. Far from it. Sure they have numbers and are one of the only groups continuing to help the wasteland(besides the followers,Eastern Brotherhood and Minuteman.) But they have many weaknesses. Sure they don't have cool power armor or flying airships(I mean like the prydwen not vertibirds) but they continue to keep fighting and are determined to return America to its glory. Although it'll take a while to recover after NV I think they'll remain for awhile as a savior to the wasteland.