How Likely Are The Space Dragon X Touch Screens To Fail And Leave Astronauts In Trouble?

First of all, SpaceX does not play in service. Its touchscreens have internal backup batteries. So even with an electrical problem, they can still work — depending on the situation, of course. But it is good to make one thing clear: if the problem is so severe that even the batteries cannot activate the screens, buttons and physical switches would be turned off, too. That is why there are redundant electrical supply systems. And that makes Dragon a lot safer than other capsules made so far.