Believe it or not, NASA had already figured out this contingency — long before the Lisa Nowak incident:

It turns out NASA has detailed, written procedures for dealing with a suicidal or psychotic astronaut in space. The documents, obtained this week by The Associated Press, say the astronaut’s crewmates should bind his wrists and ankles with duct tape, tie him down with a bungee cord and inject him with tranquilizers if necessary.

"Talk with the patient while you are restraining him," the instructions say. "Explain what you are doing, and that you are using a restraint to ensure that he is safe."

The instructions do not spell out what happens after that. But NASA spokesman James Hartsfield said the space agency, a flight surgeon on the ground and the commander in space would decide on a case-by-case basis whether to abort the flight, in the case of the shuttle, or send the astronaut home, if the episode took place on the international space station.

Good to know they’ve thought this one through.  Of course, they probably still don’t know how to handle a psychotic computer.