I figured they were trying to make themselves immortal, not erasing their physical form from Nirn?
They were already bound to the Heart when it was activated. They didn't want immortality on Nirn, because they saw it as a prison/trap. They wanted to escape it and go back to being what they used to be.
Huh. Same thing all the other elven races want right? Freedom from the stasis of the mortal plane? --- "Eternal chaos comes with chocolate rain. CHOCOLATE. RAIN!" Pinkie Pie Royal Weapons Smith of the OoT 3D board