If it is still in your interest, I’ve came up with a quite easy solution.
Perhaps this can be an option in a new release?
For now: You have to change the following if claue in sgr-nextpage-titles.php
if ( $page === max( array_map( 'count', $subpages ) ) ) {
$multipagenav = '<div class="multipage-navlink">' . __( 'Back to: ', 'sgr-npt' ) . ' <a href="' . get_permalink() . '">' . $subpages['title'][ 0 ] . '</a></div>';
} else {
$multipagenav = '<div class="multipage-navlink">' . __( 'Continue:', 'sgr-npt' ) . ' <a href="' . $this->get_subpage_link( $page +1 ) . '">' . $subpages['title'][ $page ] .'</a></div>';
}
with
if ( $page === max( array_map( 'count', $subpages ) ) ) {
//prev and first
$multipagenav = '<hr/><div class="multipage-navlink" style="text-align: left; float: left;">' . __( 'Previous:', 'sgr-npt' ) . ' <a href="' . $this->get_subpage_link( $page -1) . '">' . $subpages['title'][ $page -2 ] . '</a></div>
<div class="multipage-navlink">' . __( 'Back to: ', 'sgr-npt' ) . ' <a href="' . get_permalink() . '">' . $subpages['title'][ 0 ] . '</a></div>';
} else if ( $page != 1 ) {
//prev and next
$multipagenav = '<hr><div class="multipage-navlink" style="text-align: left; float: left;">' . __( 'Previous:', 'sgr-npt' ) . ' <a href="' . $this->get_subpage_link( $page -1) . '">
' . $subpages['title'][ $page -2 ] . '</a></div>
<div class="multipage-navlink">' . __( 'Next:', 'sgr-npt' ) . ' <a href="' . $this->get_subpage_link( $page +1 ) . '">' . $subpages['title'][ $page ] .'</a></div>';
} else {
// next
$multipagenav = '<hr></hr><div class="multipage-navlink">' . __( 'Next:', 'sgr-npt' ) . ' <a href="' . $this->get_subpage_link( $page +1 ) . '">' . $subpages['title'][ $page ] .'</a></div>';
}
Perhaps some others find this useful, too.