Help! My #MineCraft Project Disappeared!

Justin has been working merrily on rebuilding the Empire State Building on MineCraft during his Innovation Project time. With one week before the due date, he came to me to tell me it's gone.

I know nothing about MineCraft, so I can't help him.  I have questions. Can you help me with answers?

• Is this typical? 
• How does this happen?
• Is it possible to retrieve his project?
• How do we fix it?

Thanks for your help! Justin thanks you for your help!