Always make a backup of database and the directory. Store them in a zip file. Get the backup running and working on a local development environment, and make another backup of this working copy. This way you can always return to a known working copy.
If any of the crucial modules don't work, then verify the add-on compatibility, but you will be able to keep the production website running on the version that works.
To temporary disable all extensions in 2.8, use the
hidden config variable
$config['allow_extensions'] = 'y';
and uninstall the offending extension for the time being.
When a new version of the add-on becomes available,
repeat the process (of setting up a local working version)
but prior to updating EE, first update the add-on for a smooth transition.
Troubleshooting on a lower level, does require knowledge of PHP and the system.