When upgrading from Sitecore XP version 8.0 Initial Release (rev. 141212) to the version 8.0 Update-1 (rev. 150121), presentation files used by MVC-based websites might be lost in case these files are stored in the /Website/Views folder.
This happens because the above mentioned folder is deleted during the upgrade process.
The content of the /Website/Views folder is automatically backed up during the upgrade process. It can be manually restored from the following location:
/Website/temp/__UpgradeHistory/Upgrade_Sitecore 8.0 rev. 150121_<timestamp>/deleted/Views