Order by the first array within a meta_query

You can use get_posts() for both event types and merge them.

$merged_events = array();

$upcoming = get_posts(array(
    /* Your upcoming events args here. */
));

$past = get_posts(array(
    /* Your past events args here. */
));

$merged_events = array_merge( $upcoming, $past);

foreach( $merged_events as $merged_event ) {
    //Your loop
}