On the contrary, their stock valuation is staggering. If it simply increases to eclipse normal companies they can burn all they like.
It's more than a bit like a tipping point for the moral soul of market capitalism (to the extent that's not already an oxymoron).
Basically Uber will continue to dominate so long as being a complete, total monster is MORE important than any other consideration. That's what's propping them up: their continued existence is an indication that, to global capital as it exists today, the various considerations of business all boil down to one single Darwinian consideration: what will make the most money, all else aside.
Uber is a vote for 'all else aside'. They're a vote for literally capital crushing everything else before it, for the belief that abstracted power (in the form of money) can always do anything it wants. In a sense it's a vote of confidence in the freest of free markets: as long as everybody continues to believe, logically Uber can never fail because they can always out-scumbag everybody else and if you're certain that's the key to success it's illogical to break faith with 'em. That doesn't mean 'liking' it: you can hate it and still believe that's the only way to success.
The one crack in the support beam: this literally requires everyone to agree, because the ONLY thing holding Uber up is the collective confidence in their valuation. They can only burn infinitely if they represent something vitally important to capital as a whole. This is why they're still Uber, and it's pretty revealing.
But it requires just about unanimous agreement that Uber is the way of the future. It doesn't take many defectors before Uber stops making the rules for being a unicorn darling trend-setter: and people do have a sense of what's at stake here. If Uber is NOT the future… then they lose a LOT of money.
Uber is the Enron model. They are incapable of crumbling, or dwindling. They can only be the way of the future and the one model for everyone going forward… or explode, very suddenly and catastrophically.