Spoiler And without ncr income vegas dies.
*Spoiler*
If you don't want spoilers on Lonesome road, you'd best get off the page as it is on the spoiler forum.
Ulysses doesn't care about Vegas, in fact, if you do a Mr. House playthrough in LR, and I have, he states that Vegas is nothing more than a twisted city with "pre-war ghosts". But quoting Ulysses:
"Some say that war never changes. Men do, through the roads they walk". You can eventually convince Ulysses that "just as I brought the Divide to life, I can bring Vegas to life", and in my opinion is one of the few endings where you will actually come to terms with Ulysses. Well, kinda. He still sits at the entrance to the divide and QQ's for the rest of his life.
In my honest opinion, however, blowing the long 15 (essentially the backbone of the NCR), to hell will set back Vegas somewhat, you are correct in that manner, but its surviving citizens, who are lacking a real government, will flock to New Vegas. I think the destruction in the NCR will also encourage some in the east to start moving west.
I, honestly blew up both. We can now expand, unopposed. Mwahahahahaha! -> "The House Always Wins"