The OS X upgrade couldn't be started because the disk is damaged and can't be repaired My relative was attempting to upgrade her Macbook Pro and it failed. Everytime the laptop boots up, it brings up OS X Installer. The Installer never completes installation because it says the disk is damaged and cannot be repaired. 

I cannot boot into recovery mode. Probably because there isn't a recovery partition? When I hold down option on startup, the only disk that shows is OS X Installer. 

I am Windows/Linux user and not very familiar with Apple computers. What do I do to recover the data and revert everything back to normal?
Apple has two simple articles listing the exact steps needed to fully erase your startup disk and get a clean OS installed from the Mac App Store:


https://support.apple.com/kb/PH21973
https://support.apple.com/en-us/HT204904


The first (PH21973) is shorter and to the point and the second has many helpful pictures, explanations and links to other resources. You should expect about 10 minutes to print out and read through the instructions, 10 minutes to do the wipe and an hour or so to download and reinstall the OS. If you have a very slow internet connection or Apple's servers are slammed due to it being the day of a major iOS or OS release, you might need 4 hours or more to complete the OS X download.

Also - some apps like iLife and iWork are not included in OS X even though they came with your Mac initially. Be sure you back them up or verify they show up as purchased apps if you don't want to have to buy them again. AppleCare can help if you can't find your purchases or need a backup.