The information about the blocks are saved in the "block" table. The block information is saved in the admin form handled by block_admin_display_form() using the following code.
foreach ($blocks as $i => $block) {
$key = $block['module'] . '_' . $block['delta'];
$form['blocks'][$key]['module'] = array(
'#type' => 'value',
'#value' => $block['module'],
);
$form['blocks'][$key]['delta'] = array(
'#type' => 'value',
'#value' => $block['delta'],
);
$form['blocks'][$key]['info'] = array(
'#markup' => check_plain($block['info']),
);
$form['blocks'][$key]['theme'] = array(
'#type' => 'hidden',
'#value' => $theme,
);
$form['blocks'][$key]['weight'] = array(
'#type' => 'weight',
'#default_value' => $block['weight'],
'#delta' => $weight_delta,
'#title_display' => 'invisible',
'#title' => t('Weight for @block block', array('@block' => $block['info'])),
);
$form['blocks'][$key]['region'] = array(
'#type' => 'select',
'#default_value' => $block['region'] != BLOCK_REGION_NONE ? $block['region'] : NULL,
'#empty_value' => BLOCK_REGION_NONE,
'#title_display' => 'invisible',
'#title' => t('Region for @block block', array('@block' => $block['info'])),
'#options' => $block_regions,
);
$form['blocks'][$key]['configure'] = array(
'#type' => 'link',
'#title' => t('configure'),
'#href' => 'admin/structure/block/manage/' . $block['module'] . '/' . $block['delta'] . '/configure',
);
if ($block['module'] == 'block') {
$form['blocks'][$key]['delete'] = array(
'#type' => 'link',
'#title' => t('delete'),
'#href' => 'admin/structure/block/manage/' . $block['module'] . '/' . $block['delta'] . '/delete',
);
}
}
Using $form_state['values']['blocks'][$key]['module'], and $form_state['values'][$key]['delta'], you can find the block information from that table, and set the form fields to the values found in the database. In the submission handler for that button, you should also set $form_state['#rebuild'] to TRUE to rebuild the form with the restored values.
