Filter the hreflang urls and remove any that are indicative of draft or otherwise non-published content. Assumes that linked translations that are not yet published will show up as /?p=123 instead of pretty permalink.

multilingualpress-filter-draft-hreflangs.php

<?php
/**
 * Filter the hreflang urls and remove any that are indicative of draft or otherwise non-published content.
 *
 * Linked translations that are not yet published will show up as /?p=123 instead of pretty permalink.
 *
 * @param array $urls the array of language => url hreflang urls.
 * @return array
 */
add_filter( 'multilingualpress.hreflang_translations', 'filter_mlp_hreflang_translations' );
function filter_mlp_hreflang_translations( $urls ) {

	foreach ( $urls as $lang => $url ) {
		if ( false !== strpos( $url, '?p=' ) ) {
			unset( $urls[ $lang ] );
		}
	}

	return $urls;

}