One of the reasons I think that any such project in this area will likely be reasonably successful is that Vegas' population (going by Clark County, at least) has roughly doubled since the Desert Wind was axed. That gets non-tourist business, and the tourist business is also going to be helped by the often-expensive cost to drive between the locations plus the erratic times involved in the trip (both within the LA basin and on I-10/15 outside it).
To be fair, if I was given a choice between the Desert Xpress package, with its oddball terminus (Victorville or Palmdale) and what have you, and a Desert Wind (semi-)corridor project aiming for 3-5x daily frequency that serves LAX (and potentially one or more stops in the LA area), I'd probably choose the latter. But sadly, the latter doesn't seem to be happening (why it hasn't seriously been pursued, I'm not sure, but I'm inclined to blame CAHSR vacuuming all the attention CA has to spare up).
As to a "failure" of the DX project, let's not forget that there are several degrees possible there:
(1) The train covers operating costs and loan interest, but can't cover paying the loan back.
(2) The train covers operating costs, but can't cover debt service.
(3) The train fails to cover operating costs narrowly.
(4) The train fails to cover operating costs by a wide margin.
#1 and #2 probably result in the government taking an equity stake in the project during a bankruptcy. #3 may trigger a bankruptcy of some sort, but it and 1-2 would likely be eased eventually by some sort of extension down the Antelope Valley Line towards/all the way to LAX. And #4 would likely result in either a takeover by CAHSR (should that be moving along) or Amtrak not having to worry so much about replacing the Acelas (presuming that DX goes in for CAHSR/Acela II equipment).
For what it's worth, I expect #1 is the most likely result pending extension into the LA basin. Debt service is probably going to run at least $150m/yr in interest; paying back $5.5bn is going to be a stretch as well absent an inflationary surprise. #2 is almost as likely, but I think the operation should be able to cover costs based on a lot of what I've seen, likely preventing 3/4 from happening.
Capitol Limited (7), CA Zephyr (4) Lake Shore Limited (1), Acela (2), NE Regional (2), Sliver Meteor (4)
Upcoming: Silver Meteor (1), Lake Shore Limited (1), SW Chief (2), MO River Runner (1), Texas Eagle (1)
Possibly Upcoming: Either Texas Eagle (1), Capitol Limited (1), Silver Meteor (2) or Texas Eagle (1), Capitol Limited (1), Silver Meteor (1)