Hi Guys, I finally found a fix for this issue.
So after waiting for almost 4 hours I gave up and force closed my Macbook Pro. I restarted it and the mac failed to boot up showing me some kernel commands. Got me really scared as I didn't take any backup of my files. These are the steps I took to successfully install High Sierra without losing any data.
1. Restart your mac in to Recovery Mode by holding down the Command (⌘) and R keys during startup.
2. Go to disk Utility and run the First Aid for Macintosh HD. Make sure your mac is connected to WIFI.
3. Restart again but this time in the
Internet Recovery Mode by holding down Command (⌘) – Option (⌥) – R. It will take some time (10 minutes or so) to finish this process. When finished it will take you back to the normal recovery mode automatically.
4. Now Select Install a new copy of MAC OS. It will take 45 minutes to install here. After completing this process your MAC will restart and do the installation again for 45 minutes. ( I don't know why it happened two times but both the times it was real quick and it didn't freeze anywhere.)
I think the Internet recovery thing does something to fix this issue. My mac is now upgraded to High Sierra with all my files intact.
