pdo_mysql removed on updating to 16.04
At this stage I would simply recommend "turning it off and on again" by doing:
sudo apt-get purge php-common php5-common
followed by
sudo rm -r /etc/php
And then reinstalling PHP 7.0 and mysql modules:
sudo apt-get install libapache2-mod-php php-mysql
You may also try just purging and reinstalling mysql modules, first removing the package:
sudo apt-get purge php7.0-mysql
And the installing them again:
sudo apt-get install php-mysql
In both cases it's important to use apt-get purge
instead of apt-get remove
to delete any existing configuration files and package states.
The least destructive way would be trying to re-enable mysql modules using phpenmod
command:
sudo phpenmod mysqlnd pdo_mysql
It's hard to give you correct advice if we don't know what mayhem you created on your system.