V3 rollback

First, I would like to say thank you to everyone who has helped me understand V3 updates. I am new to this, and I am trying to understand V3 updates. Who better to learn from than people on a developer network with multiple years of experience.

The last question I can think of(for now). If you are running a V3 update and it fails, what happens to the data that was being transferred? I think the better question would be is.. If a V3 update fails, what has to be done to fix the update without losing data.

Thank you,

Matt