Yeah, I remember that one. It happens to me every single time. There were only two ways out of it. The first one you've already explained above. The second was to go through the entire sequence again and again for 3-4 times. Then Kreia disappears and the door to the chamber with Revan's ghost is unlocked. The problem with the second option is that it only seems to work half of the time. The other half of the time, I have to choose the "Apathy" option.
That is not the only possible glitch in the Korriban cave. When you enter the chamber with the Republic soldiers waiting for the Mandalorians to attack...after killing all the Mandalorian soldiers, everyone is supposed to just fade away, but the Republic soldiers don't fade; they're still standing there, with all the doors leading to and out of the chamber still locked. Upon speaking to the Republic soldier captain, the entire sequence repeats itself from the "...And now, we fight!" point. Only after killing the Mandalorians a second time, does the story move forward.