We dont have any numbers for the night elf population and we have no idea how many are saved so just stop. All we know is in Elegy all the remaining people were in the Temple which cant house thousands.
Kaelthas didn’t even go to the maw and he sold out the world to the Legion and was going to slaughter everyone including his own people. If he didn’t go to the Maw Sylvanas wouldn’t under normal conditions.