Ulquiorra did not die after his battle with Ichigo. Turning into an incorporeal existence similar to a spiritual body, he watched the Arrancar die and saw through Aizen's original psychology of just using the Arrancar as a tool. Then be reborn. Can you live a different and wonderful life this time?
We can only try our best to ensure that the characters are not destroyed. =V=
Another: Currently overhauling ING