Yes and no. In terms of whether something is "sustainable", "alive", "dead", or even "a good idea", market share is irrelevant. If they have 1% market share, but turn a good profit on their investment, then they would be idiots not to carry on.
The real point is when you say "losing hundreds of millions of dollars". If they are losing money, then sooner or later they have to stop, regardless of market share.
I accept that there is often an amount of correlation between market share and whether a product makes a profit, but let's not forget that it's perfectly possible to make a good profit on a very small market share, or make a massive loss on a large market share.