Don't know if it's a bug or intended however if while taming the voidwyrm kills you. You will be unable to remount it however another member of your tribe with mutagen will be able to take over and continue the taming process. Wear decent armor and heal while mounted to this void wyrm. Tames can tank them very easily while you hide behind it the lightning that it breaths out will usually hit the thing Infront of you and not pass through it like you would think. When mounted press when the text tells you too not when the void does its action you will miss it.

Finally try and get them away from the wall where the loading happens. This will cause you to miss attempts.

More Voidwyrm Taming & KO Tips