As pointed out by Jim Geraghty in the Campaign Spot, this is probably Hillary's only chance at ever being President. If she loses this year, she will probably never have another chance. This is as favorable a year for the democrats as we've seen in decades. Even 1992 might have been different if it had been a two-way race. If Hillary doesn't get it now, she will face the prospect of either running in 2012 against an incumbent Republican or running again against Obama. In either scenerio she will face tremendous up-hill odds.
If she loses Texas, any realistic chance of her recovering is probably gone. Nevertheless, I think Hillary will fight to the bitter end. As long as Obama doesn't have a majority of pledged delegates, she is going to try to win. After all, this is the Clintons we are talking about.