Did Commander Riker kill Countess Bartholomew?

Answer 1

It is impossible to know.

Professor Moriarty and Countess Regina Bartholomew were two sentient beings created in the holodeck of the U.S.S. Enterprise, NCC-1701 D. Their sentience, and rights as sentient beings, were acknowledged by Captain Jean-Luc Picard, and not disputed by anyone.

In fact, Starfleet looked into the issue.

In a situation that was more of a misunderstanding, it was necessary for Captain Picard to confine Moriarty and Bartholomew to a small computer module, in the form of a cube. Within it was programs that allowed the two of them to experience things as if they were actually roaming about the galaxy. At the end of "Ship in a Bottle," Lt. Reginald Barclay put it away, with no future references made to it.

It is unknown if the module was still aboard the Enterprise two years later in its destruction on the planet Veridian III, seen in the film Star Trek Generations. If so, it was likely destroyed with the rest of the ship, the programs "dying" as soon as the module lost power.

If the pair did die, it was done by accident or negligence rather than any intentional actions.