Retrieve ACF data if plugin is ever deactivated or uninstalled.

acf-fallback-functions.php

<?php
/**
 * Should ACF ever become disabled or deactivated for any reason
 * these functions will ensure that nothing dies in the process.
 *
 * These functions were inspired by {@author Steve Grunwell} and
 * {@author Bill Erickson}. Their work can be viewed, respectively,
 * at {@link https://stevegrunwell.com} and
 * {@link https://www.billerickson.net}.
 *
 * @author Davey Jacobson <daveyjake21 [at] geemail [dot] com>
 */
if ( ! defined( 'ABSPATH' ) ) exit; // exit if directly accessed 

if ( ! function_exists( 'get_acf_field' ) ) {
    /**
     * Get a custom field stored in the ACF Plugin.
     *
     * By running this function, we ensure that we don't die if ACF is
     * uninstalled/disabled (and thus the function is undefined).
     *
     * @author Steve Grunwell
     * @link https://stevegrunwell.com/blog/using-advanced-custom-fields-for-wordpress
     *
     * @global WP_Post|object $post The current post object.
     *
     * @see get_field()
     * 
     * @param string     $key     The key to look for (e.g. field name)
     * @param int|string $id      The post ID (int|str, defaults to $post->ID)
     * @param mixed      $default What to return if there's nothing
     * 
     * @return mixed
     */
    function get_acf_field( $key, $id = false, $default = '' ) {
        global $post;

        $key    = trim( filter_var( $key, FILTER_SANITIZE_STRING ) );
        $result = '';

        if ( function_exists( 'get_field' ) )
        {
            $result = ( isset( $post->ID ) && !$id ? get_field( $key ) : get_field( $key, $id ) );

            if ( '' === $result ) {
                $result = $default;
            }
        }
        else // get_field() is undefined, most likely due to the plugin being inactive
        {
            $current_field_value = ( isset( $post->ID ) && !$id ? get_post_meta( $post->ID, $key, true ) : get_post_meta( $id, $key, true ) );

            if ( is_int( $current_field_value ) && 'attachment' === get_post_type( $current_field_value ) )
            {
                $type = get_post_mime_type( $current_field_value );

                if ( '' === $default )
                {
                    if ( strpos( $type, 'image' ) )
                    {
                        $default = wp_get_attachment_image_src( $current_field_value, 'large' );
                    }
                    else
                    {
                        $default = wp_get_attachment_url( $current_field_value );
                    }
                }
            }
            else
            {
                if ( '' === $default )
                {
                    $default = $current_field_value;
                }
            }

            $result = $default;
        }

        if ( '' === $result )
        {
            if ( is_user_logged_in() )
            {
                return "This field contains nothing or doesn't exist (anymore).";
            }
            else
            {
                $result = 'Content coming soon.';
            }
        }

        return $result;
    }
}

if ( ! function_exists( 'get_acf_repeater' ) ) {
    /**
     * Get specified `$fields` from the repeater with slug `$key`
     *
     * @author Steve Grunwell
     * @link https://stevegrunwell.com/blog/using-advanced-custom-fields-for-wordpress
     *
     * @global WP_Post|object $post The current post instance.
     *
     * @see get_custom_field()
     * @see has_sub_field()
     * @see get_sub_field()
     *
     * @param string  $key    The custom field slug of the repeater.
     * @param array   $fields The sub-fields to retrieve.
     * @param integer $id     The post ID (will use global `$post` if not specified).
     * 
     * @return array
     */
    function get_acf_repeater( $key, $fields = array(), $id = null ) {
        global $post;

        if ( ! $id ) $id = $post->ID;

        $values = array();

        if ( ! is_admin() ) { // If ACF is ever uninstalled and/or we're on the frontend.
            /**
             * Retrieve `repeater field` content without ACF
             *
             * @author Bill Erickson
             * @link https://www.billerickson.net/advanced-custom-fields-frontend-dependency/#gist14349968
             */
            $rows = get_post_meta( $id, $key, true ); // <= The number of total `$rows`.

            if ( $rows )
            {
                $value = array();

                for ( $i = 0; $i < $rows; $i++ )
                {
                    foreach ( $fields as $field )
                    {
                        $meta_key   = "{$key}_{$i}_{$field}";
                        $meta_value = get_post_meta( $id, $meta_key, true );
                        $meta_value = do_shortcode( $meta_value );

                        $value[ $field ] = $meta_value;
                        if ( ! empty( $value ) )
                        {
                            $values[ $i ] = $value;
                        }
                    }
                }
            }
        }
        elseif ( get_acf_custom_field( $key, $id, false ) &&
             function_exists( 'has_sub_field' ) &&
             function_exists( 'get_sub_field' ) ) {

            while ( has_sub_field( $key, $id ) ) {
                $value = array();

                foreach ( $fields as $field ) {
                    $value[ $field ] = get_sub_field( $field );
                }

                if ( ! empty( $value ) ) {
                    $values[] = $value;
                }
            }
        }

        return $values;
    }
}