PHP: Deactivates a plugin (itself) if another plugin (plugin parent) is deactivated.

deactivate-plugin.php

<?php

add_action( 'update_option_active_sitewide_plugins', 'pluginprefix_deactivate_self', 10, 2 );
add_action( 'update_option_active_plugins', 'pluginprefix_deactivate_self', 10, 2 );
/**
 *  Deactivate ourself if Addthis is deactivated.
 * 
 *  @param mixed $old_value The old option value.
 *  @param mixed $value     The new option value.
 */
function pluginprefix_deactivate_self( $plugin, $network_deactivating ) {
	// The parameter/argument is the plugin basename for the parent plugin
	// In this case, we are watching the AddThis plugin
	// Note, this code will not work if the folder uploaded is a different slug (e.g., uploaded manually with custom folder name)
	_wps_deactivate_self( 'addthis/addthis_social_widget.php' );
}

if ( !function_exists( '_wps_deactivate_self' ) ) {
	/**
	 *  Deactivate ourself if parent plugin is deactivated.
	 * 
	 *  @param string $plugin_basename Plugin basename of the parent plugin.
	 */
	function _wps_deactivate_self( $plugin_basename ) {
		// Check if parent plugin is active
		if ( !is_plugin_active( $plugin_basename ) ) {
			// Parent is not active, so let's deactivate
			deactivate_plugins( plugin_basename( __FILE__ ), true );
		}
	}
}