WorkflowInstanceTable::getIdsByTemplateId

static function getIdsByTemplateId(int ...$tplIds)
{
	$filterKeyPrefix = count($tplIds) < 2 ? '=' : '@';
	if (count($tplIds) < 2)
	{
		$tplIds = reset($tplIds);
	}

	$rows = static::getList([
		'select' => ['ID'],
		'filter' => [
			$filterKeyPrefix.'WORKFLOW_TEMPLATE_ID' => $tplIds,
		]
	])->fetchAll();

	return array_column($rows, 'ID');
}