Can't restore backup

I was just running updates on my theme and I used the cog to delete the theme thinking this would disable the message but its deleted the theme which has taken my site down - I have tried to restore the backup I made this morning but it gets to 40% then displays an error message.
Then I managed to get to 80% through restoring the backup, so the site is backed up but it's missing some images, pages etc because it then failed.
We also tried to restore it manually by using the backup archive and snapshot-installer.php, but it doesn't proceed to the Deployment step.