Internal keyboard + touchpad stopped working, on Macbook air 'early 2014', Yosemite 10.10.2
Apple doesn't package the drivers or installers, so the best you could do is try these installs.


Download the latest "Combo" updater for 10.x.x and install that package.
Download the entire Yosemite Installer and then re-install the OS.


The only downside to option #2 is you need to download more data. It is the sure fire way to ensure everything is up to date. The only downside to #1 is that it might not work. Not everything is packaged in the combo updater - just the things that were updated. So if you choose that, you might waste the time downloading the small package and trying to install it.

Before you do anything, try rebooting in safe mode. That would disable any third party kernel extensions and let you know if the core OS is the problem. If the keyboard works there - you might just need to uninstall your VM and other modifications.